Golden Rule
If in doubt, keep it simple. Three pieces. One dark, one mid tone, one light. I cannot believe how often this is overlooked, and people end up looking like a big, washed-out old sock, covered head-to-toe in mid tones. (It sometimes works, but very rarely)
Bonus piece of advice - If you are wearing one statement piece, that’s enough. (Loud, jazzy, edgy, whatever you want to call it) You don’t need every single item to make a statement, because you’ll end up looking like a thrown together mess.