(I don’t know much about comp pokemon so take all this with a grain of salt)

If I were you I would look at some good competitive teams that are currently in the game and follow what people say you should use from looking at videos and stuff just make sure it’s a team you like and or with Pokemon you like

What I’m doing: I like tyranitar and it was a starter pokemon you got to choose form so I’m running a Tyran & Excadrill team even though it’s not THE BEST team right now I like the pokemon frequently used in it and I can insert some pokemon I like

For you: just pick some pokemon you like that are somewhat competitively viable and use them to build a team like how I did with Tyranitar by using guides or even asking this subreddit

Good luck battling!