How to build upon initial advantage in middle game?

Pre Move Checklist:

1. Make sure all your pieces are safe.
2. Look for forcing moves: Checks, captures, threats. You want to look at ALL forcing moves (even the bad ones) as this will force you look at, and see the entire board.
3. If there are no forcing moves, you then want to remove any of your opponent’s pieces from your side of the board.
4. If your opponent doesn’t have any of his pieces on your side of the board, then you want to improve the position of your least active piece.
5. After each move by your opponent, ask yourself: "What is my opponent trying to do?"

Middlegame Planning:

1. Expand your position:
2. Gain more space.
3. Improve the position of your pieces.
4. Decide on what side of the board to play.
5. Queenside: a-c files.
6. Center: d-e files.
7. Kingside: f-h files.

            Compare, space, material, and weakness(es)

            Play where you have the advantage.

3. DO NOT HURRY. Regroup your pieces, and be patient.

Thanks for the response. These are really good points, however I find the concept of "improving the position of pieces" quite vague. I don't understand what would make the position better after initial development is done.

My plan is mostly trying to attack the king and when I cannot find any way to do so, I find myself stuck at a position and lose from there.

In order to attack you need to have 3 of the 4 following advantages:

1. Space.

2. Material.

3. Piece Activity.

4. Weakness(es) in the opponents position.

Improving the position of a piece simply means that you are making it more active.  Take the game you posted for example.  2 candidate moves to consider.

Well first of all you are up two pawns which is nice. I wouldn't say he has any kind of real compensation either. Your queen rook and bishop are looking good, but your knight and especially your a rook need to join the game. The problem is these pieces are a bit tied up.

This is a rare case where you actually may want to consider a5, a4, Ra4 for development. If he finds a way to defend his d pawn - which will be difficult - you can then play Rc5, and now that the c7 pawn is no longer under attack, you can develop your knight to f6.  Note that Ne6 may come at any time which would be interesting. I think you will just end up exchanging and regaining the pawn since the immediate Bc4 is not on the cards, and your pieces can encircle the pawn - Ng7, Re8. This might be white's best try though because if you trade the light square bishop, they can use their light bishop to attack your light squared weaknesses.

Nf6 immediately looks good as well. If Rxc7, Nxd4, Qb3, Qe1#

I have been coaching part time the last 3 years and I have a lot of experience getting beginners to 1800 level or so and even higher. I am willing to offer you a free 30 minute session if you are serious about improving. Feel free to message me.

Really nice info, we would keep in mind next time, thanks guys