Yeah, that's a common feeling... probably for every level.
It's... hard for me to write a simple answer because you're basically asking how to play the middlegame... which is better answered by reading whole books.
But ok, I'll try to shorten it to something simple. Lets take king safety and piece activity as too obvious to talk about. They are your #1 and #2 priorities, but often your king will be pretty safe, and you should already know piece activity is extremely important all game long.
So with those out of the way the early middlegame is often about deciding on a pawn break. A pawn break is a move that will force a pawn trade. When pawns are traded lines (files, ranks, and diagonals) are opened up (meaning pawns aren't blocking them anymore). Your pieces will use these newly opened lines to increase their activity and ideally infiltrate onto your opponent's side of the board.
So what does an ideal pawn break look like? It will be in an area where
1) Your pawns are more advanced than the opponent's in that area
2) You have a higher number of pieces (or more active pieces)
Here's an example from a pawn structure typically seen in the French advance
Black is basically required to play the pawn break c5 at some point. His d pawn is not further up the board than white's (both pawns have moved 2 squares) but the queenside is where black's pawns claim more territory.
Similarly, if white goes for a pawn break it is often on f5. Sometimes this taught as playing a pawn break where your main pawn chain "points." Black's pawns "point" to the queenside and white's to the kingside.
Here's another example
Here white's pawn breaks are on c4 and g4. Black's are on c5 and g5.
In this case the pawn aren't "pointing" so the players will choose based on their piece activity. If white has many pieces on the queenside, then he will probably prefer c4. If black sees most of white's pieces are on the queenside, he might decide to try attacking on the kingside with a g5 pawn break.
Pawn breaks don't have to be on opposite sides though. It's possible for both c4 and c5 to be played, and the players will fight to see who can do better on the queenside.
Hi everyone/someone/anyone!
For a little while now, I've noticed a big weakness in my game is in the period from the opening ending and the middle game beginning. There are maybe one or two openings I know fairly well for the main lines, that's ok. I do really well (for my ability) with puzzles and those things, so I reckon I'm fine when the middle game opens up a bit.
When it comes to finishing the opening though, I'm familiar with how positions look but I'm often looking for the way forward. Like, I've achieved the position I know I should have reached or I can see my pieces are developed and even my opponent doesn't have any clear breakthroughs and it leaves me wondering, "ok, opening seems to be fine but how can I get out of the opening and into the middlegame still on equal terms?"
This is when I feel like I'm prone to mistakes and enter the middle game disadvantaged. Does anyone have any ideas on resources, books or anything of the sort that addresses this type of situation? Is this a common thing?