Once you play a game, most seem to get the gist of it.
Basically, you make a list of all your battle ready pokémon. Tiers don't matter and legends are fine (I don't use them but saying if you do since people ask about that when battling). The only thing that I will not battle against are hacks, even if they're within the rules of the game. However, exceptions are clones, altered to change ball/name (wish this was possible in game), or even painted shinies. Also while I'm not for it, if the only thing in a pokémon's family tree that's not legit is just one of the unfortunately popular hacked 6iv dittos, those are fine. However any other hacks in the tree are not.
Once the list is made, I tend to use a dice roll/random number generator at another site I do most of my battling. This picks the 6 pokémon of our team. They should not be altered before the battle. So say you know my team would have a high weakness to electric moves, it'd be unfair to for that battle temporarily use electric move tms to give yourself the edge. Also, items should be their set items. So even if say you have multiple megas you use as such...you keep each holding their mega stone and you choose in the battle who, if any, to mega evolve.
Finally, at the team preview screen, that's where we choose our 3 from our pools to do our best in the battle. Then just do your best and have fun.
So if you give me your list of battle readies (nicknames are fine, just whatever the pokémon's name is whether it be the specie's or a nickname), I can figure out our teams. ^^