- Find the core
You gotta find whats your win condition and/or the pokemon(s) you want to shine most in your team.
-Find the best possible synergy you can get with that same core typing, stat and coverage wise
To help you protect that core and define your team's weaknesses easily.
-Try to have at least one entry hazard setup and one defog/spinner.
Entry hazard are a huge part of the game. Using it and dealing with it is a must in every team IMO.
-I try to check my "checklist" which consits of 1 Physical tank, 1 special tank, 1 physical sweeper, 1 special sweeper, 1 revenge killer, fodder for some special stuff most of the time something bulky or just a general good mon to fit the team
- Test the first team i come up with on Showdown in ladder games as well as friendly trollier games to test your team from every possible anles (around 10 to 20 games)
-Adjust my team accordingly to the tests.
-Redo previous steps until satisfied or godlike team achieved.
That's pretty much it for me.
Most important thing is to come with ne innovative things. Yesterday i fought Ary with my OU team idea. MVP was my resttalk milotic. The thing is a hidden op i think. Almost neverseen doesnt mean bad, it's just uncommon. Try stuff and have fun doing so! Thats the key to pokemon.