To complete other answers, I'd avise you to play 15 min games or longer time control, avoid blitz at the very beginning. Playing blitz is a very good way to practise opening though, and you speed thinking, but not right now.
Speaking of openings, choose an opening that suits your style (be it a
e4 opening) and stick to it. Play something sound that you intend to play in the long run. For example, a lot of players try to dodge the Sicilian playing McDonnell Attack or Grand-Prix (a bit better than the latter). Those are not totally unplayable but you won't learn a lot and will be crushed against stronger players.
You shoud avoid the most theoritical openings, because you'll spend most of you time and efforts remembering moves (or findind them over the board) rather than playing chess.
If you are a
d4 player, you'll learn (anyway!) the
Queen's gambit declined, to which you can add the
Trompovsky (very interesting opening).
If you are an
e4 player and you're afraid of the open Sicilian, give a try to the
As black, against
e4 and if you're willing to play the Sicilian, I'd recommand the
d4, it's hard to tell, you have a bunch of choice. The
Nimzo is very interesting as well, theoretical of course but maybe not as much as the Grünfeld or King's indian.
But once again, it depends on your style.