I used to lurk PokeGym a lot to keep up with what’s current but it was mostly going to my league club every week and improving from there. If you want to Win there’s like a certain number of decks any given rotation where if you play them from a long time and memorise given situations then even amateurs can do very well at tournament although in my experience except in fringe cases creativity in deck building was rarely rewards (Famous exception was the first ever world championships where the japanese players CREAMED everyone else because they released that Team Magma decks had by far the quickest setup potential in the format while the west dismissed it as a novelty).
All of this advice is at least a decade old now but yeah, have fun, see what works for you, look at what everyone else is doing and how you can do it better, rinse, repeat, etc.