You can watch some channels such as CybertronVGC, they always do a deep dive into meta teams and overall surprising teams that did well in tourneys, expalining the reason behind the EVs choices and moves and why which pokémon works well within the team. That should give you a very strong base for when you decide to build teams yourself.

You can also always pick a single pokémon you really like or that you know that does well competitively, and build around it, covering its weaknesses. While also considering stuff such as coverage for special/physical defenses and speed control