as a new player to 2d fighters, I can say starting out by playing seriously online actually HURT my playstyle. the character I picked to main was rachel... a bad choice in general for the first-time player who should be mastering the basics. i started playing online near launch, and i found i could win fairly easily by mastering her cannon moves; i guess people hadn't learned how to deal with rachel yet. i mean, i didn't ONLY spam cannon -i knew how to use wind, and pumpkin, and a few reeeeeeally basic combos. but by caring about winning rather than learning how to play the game, i got way more skilled at timing the cannon than anything else. which came back to haunt me pretty hard when people started aggressively rushing me and i hadn't learned how to block
you can't take online play too seriously -I agree with other posters who say NEVER expect to win. whenever you go in wanting to win really bad, you get more easily frustrated or intimidated by good players, and end up playing WORSE. i play my best when i see every match as a challenge to see how well I can PLAY against the opponent, whether i win or lose. i find i lose less frequently/play better when i go in with that mindset, and when i do lose -even if i get trashed- i don't get nearly as frustrated. the glory's not in victory, but in a match well-played.
besides, i think we've all seen matches where the person who played better didn't necessarily win! (tao vs. arakune, rachel vs. nu, carl vs anyone... )