The Beastmen are the corrupt children of Chaos, and are almost the epitome of everything that Chaos symbolises, anarchy, hatred and brutality. As a Beastlord, you will have many troops at your disposal, mainly Ungor, Gor and Bestigor, as well as the Tuskgors which pull the chariot. The first thing you must decide upon is who is to be your general, in smaller battles it would be advisable to take a Shaman. Although Beastman characters are remarkably cheap relative to other Chaos Characters, this is no excuse to field them as you would field a human or goblin character(i.e. as a decoy or sacrifice) as they are still quite capable fighters, and should be used in one of the two classical champion roles:
If you choose to use your characters for the first purpose, then they are best equipped
with a magic sword which either allows better chances of hitting, or extra attacks,
coupled with an extra hand weapon. For the second purpose, equip them with as much mundane
armour as you can(heavy armour and shield in most cases), and then give them a special
save, such as the Black Amulet or similar, then give them a suitable anti-character weapon
like a Boneblade, Sword of Heroes, etc. Obviously, Shamen are not going to fulfil a
battelfield role that a Beastlord would be expected to, you are better advised equipping
them to make up their points in casualties using magic, I advise the use of Dark Magic, as
this also allows you to use dispel cards as powers, so your shaman will be able to cast
more of the highly destructive spells. However, if you wish for your Shaman to fulfil some
sort of tactical magic role, then use the Chaos Decks, which are much more specialised and
tactical. The Slaanesh deck is made for picking out characters and holding regiments, so
the Shaman carrying these spells would be best used accompanying a retinue ith Minotaurs,
who can take advantage of the lack of movement to wreak carnage in the frozen targets.
Nurgle magic is very 'Orcy', it is intended for use at close-quarters. It is more of a
combat enhancing magic deck, giving the unti bearing a Nurgle Shaman that edge when it
gets into the magic phase. I advise using a spell such as Rancid Visitation to 'soften'
the target up a bit before charging into them. The best location for this sort of Shaman
is in a Chariot, allowing them to get into combat as quickly as is possible, or in a unit
of Bestigors, whose combative abilities can be complemented by the magic. The Tzeentch
spells are typically long ranged and quite destructive, and are best used to blast the
enemy from a distance, and Incandescent Assassin is especially good at picking out
characters, especially against races with low WS, as is Bolt of Change(identical to Chaos
Spawn except half the range and it kills the character instead of turning it to spawn).
For the retinue, I advise a large block of Gors, who can assist the shaman if he is forced
into combat, but with Shield of Fire and Pink Fire of Tzeentch he should remain quite
safe.
Retinues, as you can see, play an important part in the whole army. A Warlord may join any unit in the army, but be aware that in some cases this is undesirable, for instance, a Shaman would be useless in a unit with the Banner of Rage, while a Beastlord would be in the best place there, as opposed to being with Ungors. The best location for your general(who should always have the Crown of Command) is fairly central in a large block of Gors, as they aren't looked on as the most dangerous threats, so the Beastlord is safe from the majority of anti-character items, as well as being in a large unit of multiple wound troops with high toughness, which is handy for those 'Look Out Sir!' rolls, which will inevitably occur. Unless the Herd contains a number of Chariots, I don't advise putting your general in one, as this will leave him away from the main part of the Herd, leaving the army with lower leadership(unless you have another Beastlord or similar with a Leadership enhancing item), as well as placing a high concentration of points in one very vulnerable location. Minotaurs and Chaos Hounds provide excellent shock troops, as their speed and good stats allow them to move in quickly and hit the enemy giving you extra time to move your slower units up into the fray. Minotaurs in particular are excellent, with the amended Bloodgreed rules, they become even more dangerous than before, with the possibility of Frenzy giving you a massive 4 attacks(5 if you take an extra hand weapon), with their better than average WS and strength, as well as three wounds.
The Beastman units are also far from poor. the Ungors, even, are excellent troops for the mere 4.5 points you pay for them, having 4 toughness and the ability to carry spears; although their low leadership and infighting can be troubling, so always take the Beastman Champion and keep them within close proximity of either the battle standard bearer or General. In Skirmish formation, the Ungors enter a class of their own, being the only Chaos troops able to do so, which also makes them immune to infighting, as well as being harder to hit when shot at, for full details of how to use skirmishers, go here. Gors are the average Beastman, and their stats are superior to that of most other races, having a high WS, T and 2 wounds, the only let downs being the low strength and leadership(an extra attack and no infighting would be nice). I advise equipping them with extra hand weapons if facing Skaven, Elves, Empire or Goblins, or Halberds against other races. If I am facing Orcs, I occasionally even hazard to use double-handed weapons, as the low WS of the Orcs means that when the Gors get to attack, they will inflict maximum damage. Bestigors are the greatest of the Beastmen, they have awesome stats, and are only limited by their single attack and the one unit you are allowed, so make that unit as big as you can! I feel Bestigors are let down by a regular Beastman Champion, so I usually accompany them with at least a Chief. A good idea with Bestigors in large regiments is to give them the Rapturous Standard, so that they will never flee, nor be affected by any psychology so that their large numbers and awesome combative abilities will eventually tell on the foe. The Beastman Chariot is excellent, as its low points cost(relative to other chariots) enables you to take several without any great expenditure of points. Although slightly slower than the average chariot, the 'steeds'(Tuskgors) and crew are much more resilient, so they are more likely to survive combats. In each squadron of chariots, I advise taking a Chief to both boost the leadership of at least that one chariot as well as providing an excellent fighter to hack even more of any survivors to pieces after the charge has been resolved.
Certain enemies are more troubling than others when fighting them. undead would be the most notable of these, as their fear can be very damaging to an army with such typically low leadership. Against undead, always take the Crown of Command and as many characters with high leadership or leadership enhancing items as possible, as well as many Minotaurs, who cause fear and are hence immune to its effects, and are also exceedingly good at killing undead. As a general rule against Undead, always make sure your general is well equipped to take down very tough characters, as vampires and Tomb Kings are otherwise very dangerous to a Beastlord's safety. I advise giving them Heavy Armour, shield, Black Amulet, Sword of heroes and the Crown of Command, as this will enable you to deflect most of the attacks directed against you, mesmirism will work only rarely, and you will be able to strike back with strength 7 against the tougher opponents(those you would ordinarily have difficulty wounding) as well as inflicting d3 wounds on said foes. Against Undead, always keep a Shaman with Dark Magic or the Book of Ashur(taking a High Elf Spell) near to your general, as this will ensure at least some damage is done with the Dark magic against enemies who could potentially threaten your Beastlord. If you take the Book of Ashur with a High magic Spell, then you will also be able to use powers as dispels, and you may get lucky and get Drain Magic, a very useful spell against Necromantic magic.
When constructed your Warherd, centre it around the Warlords, especially a central core of Beastlords. As a general rule, always take a Shaman lord, as they may now be the generals, you can even take one in 1000 point battles, which, in such tiny battles, will allow you to control the magic against all but Undead, who will also doubtless have either a Necromancer Lord, Liche or Vampire. In battles which are slightly larger, always take Beastlords whenever you are able, as they are the best fighters you have access to(excluding the Minotaur characters) and are very cheap for what you get. As a basic rule, accompany the general with the most solid troops, e.g. large blocks of Gors, etc. While you leave your shock troops under the control of other characters. This keeps your General in a solid and stable unit, which will leave him in a good central position, so his Leadership can be used by the majority of the Herd.
A few nasty hints for using the characters in your herd: Give your general the Crown of Command and the Crown of Sorcery(OK, it's powergaming, but your general becomes really nasty); Crown of Command, Black Amulet and Sword of Heroes(the chars that will give you any trouble normally are easily dealt with by the Sword and Black Amulet); Shaman with the Forbidden Rod(Beastman Shamen have loads more wounds than normal magic users); etc. In general, equip your characters for a battlefield role, as they are not as capable as Chaos Warrior champions, they will have to specialise. Let loose the goats of war!