I tend to initially train a pokemon that I want to try out on a whim, see how it performs. Then I gauge its weaknesses and choose teammates that cover those weaknesses. I then practice with the team, noting key problems that threaten it and choose new teammates or readjust EVs/movesets to answer those threats.
Pick a few pokemon/strategies you want to use, analyse their weakness, slap in other pokemon who cover those weakness, go to the simulator, test them, indentify what are the most dangerous pokemon to your team, change it accordingly. --- 3DS FC: 1865-0018-0383