Are their any sort of guidelines defined for choosing pokes on a team? Such as balancing types, covering weakness etc.?
for an easy example, I'll use the following method of building a team:
pick a sweeper to build the team around: Say you have a Pokemon you've always wanted to throw on a team, or just something you enjoy using, or a random standard setup sweeper. You put it on the team, and decide what you need to support it with. Most sweepers will need entry hazards, as they are invaluable in helping a sweep. Pick whichever hazard user you like, and go with it. What walls your sweeper? Carry something to beat what walls it. Do you want a weather, whether it be for weather control or being beneficial to your sweeper? You might want to carry priority or a Scarfer to deal with some Scarfed checks to your chosen sweeper. Lastly, as is often the mistake with this kind of team,
have a secondary method of winning. It can be another sweeper, a powerful Choice Scarf user, or even a Life Orb attacker, just have another way to win in case something happens to your chosen sweeper.
resistances you should have: Dragon, Flying, Water, Ground, Fire, and Bug, at the very least
check for weaknesses: this is a point where you can take a look over at the usage stats. look over say the top 30-40. make sure that nothing can totally tear apart your team with you unable to check it. make sure you have a method to check whatever you find.
I hope this helps!