"Blank" middlegame aspect

In this position, black has an extra pawn and white really doesn't have anything to show for it. Could anyone provide of some principles or guidelines to follow that help in stabilizing an advantage? Also the title is '"Blank" middlegame aspect' because this stuff mostly gets skipped over in many annotations and game reviews.

ps: I played d5 and lost all my advantage

Hmm. A difficult position.

In the actual game position, your c pawn was attacked. You could have defended it with Rc8.

Or you could blast everything open with ..d5.. Well ..d5 seems pretty radical since it opens up the center and your king position is pretty open. It also may give white the use of e4 for his knight.

Well, thanks for the reminder that my postion was one with w/to move. With that being said, d5 loses all advantage according to the engine. Do I know why? Kinda. It creates two pawn weakness on c6 and e5 which fell later in the game. But the engine's correct move is Qa8(I kinda agree with this move but I don't really know why. It just kinda seems good.) Then Rf7 and moves like those waiting for the OPPONENT to make a commital decision or it atleast seems like that to me.