When selecting your weapons, you need to take quite a few things into consideration:
heat, damage, legality with the league, effectiveness, weight, ammo, range and most important of all, your own personal taste.
Find a combination of weapons that best suits your playing style and stick with them!
Always remember to swap enough ammo.
Always place as many heatsinks as possible. Try to place them in unimportant places such as the arms.
Armour is also very important. Keep these points in mind:
-Have 2/3 front and 1/3 rear.
-Never use a 'Mech that doesn't have full armour; if you're off by one, it's fine.
-A 'Mech is most stable with standard engine, standard interrior and Ferro Fibrus armour.
Always have as many Jump Jets as possible. Usually 4 or 5.