Just start playing. Be ready to get owned, cause player base is low, so it's quite probable you'll be matched with well experienced players, but practice makes perfect, so...
3v3 and 4v4 are chaotic and differ a lot from 1v1 and 2v2 (and i believe 1s and 2s are more balanced than 3s and 4s), so i would suggest you 1v1 and 2v2.
