CHAOS TACTICA
Most of the chaos troops are expensive points wise so a Chaos army will most often be outnumbered by the enemy. Because of this, it is one of the cheapest armies to buy in terms of money. And as well as it being the supreme HtH army. The Chaos army has the meanest HtH troops in chaos warriors and knights, as well as creatures such as Dragon Ogres. However, it lacks missle fire and war machines. It's only source of missle fire are centuars (which, while useful, are too expensive to rely on them for missle fire). The combination of it's obvious HtH strengths, ultra powerful greater daemons, and it being inexpensive money-wise, makes Chaos a common first choice for new and young players.
Chaos often gets a bad reputation for being an unfair or cheesy army. This simply isn't the case... at least not all of it. The problem with Chaos is it's one of the easier armies to abuse because it's power is so heavy in one direction (ie hand-to-hand combat). And while the background of the 4 gods goes against often having characters and troops from different chaos gods (especially certain combinations) in the same army. It is easy to do so... Khorne who dislikes magic is often paired in armies with Tzeentch, the master of magic, or even worse, Slannesh who Khorne despises. It's easy to combine the best aspects of each god into one army which is where most of the bad reputation Chaos has comes from. And no offense to anyone, but young kids (14 or so) often find the ability to make chaos into an awesome "best of all gods" army appealing and without meaning to be unfair, make unfair and cheesy armies without paying attention to the background story and fluff about Chaos. This not only gives other players the impression Chaos is unfair, but can scare away new players who get destroyed in their first few games by a "power gamer". Neither one is good for the hobby.
However many people who play chaos, especially those who have been playing Warhammer for a long time, will generally play a chaos army devouted to ONE god. Khorne is probably the most popular god because of his troops supreme HtH ability and the ability of the single most powerful model in Warhammer the Greater Daemon of Khorne, the BloodThirster. I decided on playing a primarily Tzeentch army. I am painting my troops (such as my warriors and knights) in Tzeentch colors and often use one of the Tzeentch daemons, the Flamers of Tzeentch. I have all 4 greater daemons, however i've only used Tzeentch's greater daemon (The Lord of Change) once. Mainly i bought all 4 greater daemon models while they were still about $14 per daemon because i refuse to pay $40 for one greater daemon model i will rarely use (no matter how nice it looks).
Anyway, below are some of my ideas on tactics for chaos (tzeentch primarily). If you have any further ideas, especially on using armies devouted to one of hte other 3 chaos gods, please feel free to e-mail me and i'll (if i can) put your ideas up.
Chaos Troops:
Chaos has great troops. Excellant in HtH. What makes them devouted to a certain god is what type of character leads their units. Although this matters little.
Chaos Warriors: These guys are great foot troops. WS6 S4 T4 A2 and Ld9 are great. Plus they can take chaos armor, which is expensive, but gives them a 4+ magic armor save (3+ with shield) and the chaos armor does not reduce their movement like heavy armor and a shield do. They also have other good options such as being able to give them halberds or double handed weapons for 2 S5 or S6 attacks respectively, or shields or a 2nd hand weapon giving each warrior 3 attacks. However at 24pts per model, giving them chaos armor and any of the other options makes them over 30pts per model. I never use them in battles 2000pts or less. And in 3K it's questionable.
Chaos Knights: These are AWESOME heavy cavalry... essentially warriors with lances and shields on barded horses (and the horses are better than most human troops). Giving them chaos armor gives you guys with 2 S6 attacks when charging (because of the lance) and a 1+ armor save! Hoever, they are already 66pts per model and 80pts when given chaos armor. Being this expensive means a unit of 5 with chaos armor (and a standard bearer) is almost 500pts. It also means that i leave them home except in rather large games.
Beastmen: In my opinion the first unit any chaos army should have. They are reletively cheap (in comparison to other chaos troops) and have T4 and 2 wounds! I take a large unit of these (20+) with doubled handed weapons and the Dread Banner magic standard being led by a beasman champion or hero with crown of command (and second magic item in the case of the hero such as a spell shield). They make a solid infantry unit with S5 attacks (their T4 and 2wounds keeps them alive long enough to survive striking last) and ranks. They are hard to kill with missle fire. I never bother with armor because anything strong enough to wound them reliably will negate a 6+ save.
Chaos Chariots: I've only used these once, but they worked well. You can choose once riden by chaos warriors or a cheaper one with beastmen. Against an army of undead i say take chaos warriors chariots because beastmen have trouble passing fear tests. Against most other armies, Beastman chariots are great, with scythed wheels.
Chaos Hounds: i've never used them and probably won't anytime soon.
Minotaurs: Again i've never used them, but with their high movement and leadership, along with 3 wounds, they could work well. however they can never puruse a borken opponent as they will feed on their beaten foes' bodies.
Harpies: Great troops for attack enemy war machines or getting flank attacks. They have a bad leadership (it's a 6, not 8 like the list says), but WS4, S4, T4 and 2 wounds and their ability to fly make them very good for killing war machine crew and flanking units. I always (if i can) take at least one unit of 5. Against undead however they will likely no pass a fear test unless kept within 12" of the general.
Dragon Ogres: The ultimate heavy cavalry. They are very strong, have a lot of wounds and attacks, plus with light armor have a 4+ save. I give them either an extra hand weapon and light armor or double handed weapon and light armor. However, with only a leadership of 7, they should be kept close enough to the general to benefit his leadership or be led by a chaos champion. They are expensive, but do not need to be fielded in units of 5. I like fielding a unit of 3. They are also a great place to spend those chaos gifts that grant extra attacks...
Centuars and Trolls: I've only used centuars once and never used trolls. The centuars didn't work out and i'd probably prefer dragon ogres to trolls.
Tzeentch Daemons: Daemons are very useful for augmenting your army. Both is magic casting and attack power. Plus they are paid out of different points than characters and regiments.
Lord of Change: The greater daemon of Tzeentch is not a HtH monster the way the Bloodthirster is. The advantage of the Lord of Change is that it is a flying, level 4 wizard that does not come out of character points and has 7 wounds. However, it is NOT invulnerable (i've had skinks with poison arrows shooting at it do 2 wounds on 5 shots before). I do not often use the greater daemon.
Pink & Blue Horrors: I've not yet used these (cause i only have 1 pink one and 2 blue). Hoever their ability to cast magic gives you an additional way to get tzeentch spells without taking a character. They can also be created (pink ones) with one of the Tzeentch spells.
Flamers: I love these things. They are very expensive (50pts each) so i only use small units of 5 or 6. However with 2 attacks and 2 wounds apiece at S5 and D3 wounds caused and a bounding movement of 9" (18inch charge), they are great. Plus their ability to shoot 6" and cause a D6 S3 hits (which count as magical attacks) makes it a risk to charge them as they can stand and shoot with great results.
Chaos Characters: Chaos characters are very expensive. So you have to pick and choose carefully where you have characters. Unlike Empire and Orcs&Goblins armies you don't have cheap characters to stick everywhere, nor do you have 75% characters allowed as do Bretonnians. The good thing is that chaos troops don't need help with leadership as much as many other armies and many chaos troops are better than some armies' characers. Each chaos character is also devouted to one god and that god grants them special favours. For Tzeentch characters (all characters, bother champions, heroes, lords and sorcerers), Tzeentch has granted them a natural magic dispell of 4+ for spells cast at the character. Some of the the troop types also have characters such as beastman and dragon ogre characters.
Chaos Champions: Chaos champs are nearly as expensive as human generals, however they are even better in combat with the exception of one having 1 wound. And unlike other race's champions, chaos champions can be armed differently than the unit. To me they are best used to boosting the leadership of units like dragon ogres and centaurs. Or for holding an important magic item.
Chaos Heroes: They have the same advantages and disadvantages of champs, but cost more. However they can also rid daemonic beasts. Which for a Tzeentch hero means he can ride a disc of tzeentch making disc riding heroes excellant for fast attack assignments. Generally however, heroes can only be afforded in large games.
Chaos Lords: Are one of the best HtH characters in the game. But they pay for it by being 3 times as expensive as a human general, and twice as much as an elf or dwarven one. It's easy to make a Chaos General into an overpowered character. I personally like to keep my general on a disc with the armor of protection (or occasionally with the chaos armor/runeshield combo) along with a decent, but not over powered magic item ( like the flail of skulls).
Chaos Sorcerer: Because a lot of the Tzeentch spells are short range damage spells i mount by tzeentch sorcerers on disc to fire their magic at units. Or to get close to characters to attack with spells and bound items. They can take either Tzeentch spells or dark magic.
Beastman Shamans: Are great extra mages. Slightly cheaper than chaos sorcerers, but with more wounds. They can also take spells from different chaos gods at ones (ie a level 4 shaman can take 2 tzeentch, 1 slannesh, and 1 nurlge spell if he wished). This is the only exception to the general rule that mages cannot combine spell decks. They can also alternately take dark magic. I field one in my beastman unit if i have enough points after adding the beastman champ.
Beastman Characters: I love these guys. I always have at least a beastman champion (but prefer a hero) in my beastman unit with the crown of command. They are also very survivable with high toughness (T5 for heroes and lords) and alot of wounds.
Minotaur Characters: I've never used minotaurs or characters.
Centuar Characters: I've never used them so i don't know if they are useful or not.
Dragon Ogre Characters: If chaos generals are the HtH gods of the warhammer world, then dragon ogre lords are the OverGods. A dragon ogre lord is probably the most fearsome character in the game. With WS7, S6, T6, 6wounds and 6 attacks, as well as being able to carry 3 magic items, this thing is truely a beast. He also costs more than a regular dragon. At 521pts for the lord and 155pts for the champion, these guys are only rarely seen and in very big battles.
Chaos Tactics:
Chaos tactics are pretty straight forward. Get into HtH as soon as possible :) you tactics are also somewhat determined by the god your army follows. A khorne army has no choice but to charge charge charge because it's characters are frenzied. I personally first take a large unit of beastmen equiped as i said before. And i take a unit of 3 dragon ogres with light armor and either extra hand weapons or double handed weapons. I always keep my general on disc close enough to the dragon ogres to use his leadership. I also love a unit of 5 or 6 Flamers. Along with harpies if my opponent fields war machines or to attack the flanks of units. I don't take warriors or knights unless the game is fairly big. I also put my tzeentch sorcerers on discs to best use their magic. And i always take tzeentch magic. I find that beastmen with the dread banner and crown of command are great for tying up a unit (even if they can't beat the unit) long enough for flamers or harpies to flank the unit. My general stays back unitl i find something suitable to kill, like enemy mages. Even without expensive magic items, he is better than most in HtH. I do not attack units with him however, unless that unit is already in combat. It's too easy to roll bad with him and be broken by ranks and standard bonus.