Midgame/locked positions

Hi, I'm quite new to chess and have been playing ~100 games or so on this site over the last few days. Also tried to get into some basic chess theory, but mostly just played games. My goal is to become better at chess, and first I'd like to reach a level where I can beat "anyone" who simply know how the pieces move and never studied any tactics or principles of chess.

I have a question regarding the midgame. In most of my games I have decent development and maintain equality into the midgame. I try to follow openings/defenses to a certain degree, but I haven't memorized any of them 100% - so at this point I basically just play whatever falls within the few tactical principles I've learned so far: center control, no doubling of pawns, never more a piece twice early etc - basic stuff.

So usually I enter the midgame in a "locked position". I don't know if this is the correct term, but I'm talking about a position where both my opponent and I have developed simularly and there is no clear advantage to any player.

Basically, I don't know where to go from here. Is memorizing openings/defenses the best way to enter the midgame in an advantageous position? The problem is that my current opponents (900-1100 rating) aren't really following strict openings/defense play themselves.

What kind of mindset should I have in the early midgame?

Attack Attack Attack.  

And regarding openings,

"Your only task in the opening is to reach a playable middlegame."

Lajos Portisch