Creating Targets in Middlegame

Yes, this is a very difficult part of chess :)  Actually whole books and videos have been made about it, strategy books/videos to be specific.  When good players play their moves are tactically sound, yes, but also they have a general idea or aim in mind.  Some positions call for an attack while others don't.  Pachman's book "Modern Chess Strategy" is a very good one.

“Tactics is knowing what to do when there is something to do, strategy is knowing what to do when there is nothing to do.” –Tartakower

The position you show has opposite side castling which almost always involves an assault on the king as an overall goal.   Strategically in an attack there are two basic aims, to open lines against the enemy king and to remove defenders (or increase attackers).

As for the specific position the first two things I notice are white has less space, and there's opposite side castling.  White can play e4 at some point if he wants, and he is contesting the center so space/the center is a non-issue.  Because of the castling (and as with all opposite side castling) as white I generally want to push my pawns (here g and h pawns) to open lines against his king.  So first I'd reorganize my pieces (keeping an eye on what black wants to do i.e. not make his job easier) and then try to open some lines on the kingside.  Bg2, Nc4, and a rook or rooks on the f, g, and/or h files are regular looking moves.  Also Kb1 is regular looking to get away from the center, shore up the undefended a2 pawn, prophylactic thinking.

Moves like a4 and d4 are the kind that help black in this position because black's most basic idea is to open lines on the queenside against white's king and by advancing pawns on that side back can play pawn breaks faster (i.e. trade pawns and open lines).