Every new game is a fresh, new, relaxed experience for me, so as of late my mindset is catching and using what I like. :) If I ever go back and do some sort of a challenge run or something, I may plan something like that, like a monotype run or just a run of solely 6 certain Pok?mon from start to finish. In the case of Sun/Moon, I already plan to at least catch and use some Pok?mon that I've found interest in (Salandit, Rockruff, Vikavolt, etc.) whenever I get them in the game.
I've lately contemplated starting new games with one or two unique Pok?mon/Pok?mon unobtainable normally in that game as a sort of "partner" Pok?mon to always keep with me. Unsure if I'm going to do that for SM, but who knows.