Teambuilding Focuses

1.) Usage statistics, both generally and for sets, should be the go-to resource while teambuilding.
2.) Test your teams, optimally against good players that can see the weaknesses. Laddering on Smogtours can probably accomplish this well, if you don't mind people watching the auto-recorded replay.
3.) Have two checks/counters to the top 10 Pokemon at least.
4.) Have two checks and/or one counter to the top 30 Pokemon at least.
5.) Have a Win Condition.
6.) Have something to fill in as a Win Condition if your first pick is wrecked by team matchup.
7.) Make sure your Hazard remover synergizes well with your SR-Weak Pokemon.
8.) Innovations/Lures you create should be usable outside of its main use.
9.) Always have a way to deal with Setup Sweepers and Fast Pokemon.
10.) You aren't going to make a good team if you aren't having fun building it; It will wear off on you while battling.