please help

hello guys ^^

i am currently rated about 1400 in blitz and i struggle going above that ... i know my problem but i dont know how to solve it ...

this is a game i had yesterday 

https://www.chess.com/live/game/2142980751

i usually play perfectly and find the best move till the middle game ( even in the middle game if my opponent has a weakness which i will make my target ) , then theres that moment in the middle when the opponent has no weaknesses that's when my brain freezes and i never find the answer to " what next " 

look at my game yesterday till move 20 ... i had clear advantage i put myself into , but everything then collapsed , and till now i still dont know what i had to do 

and even now , i still cant find the idea of what shall i had done next ? what shall my objective be ? 
please help me , i started learning chess last October and i am trying to improve , but i have been struggling for like 2 month at this rank , finding it very hard to solve this question " what is next " 

thanks in advance for anyone who will reply , have a nice day ^^

if you can't find a weakness make one. attack the king. 

although this probably isn't good advice, try castling opposite sides to the opponent and do a pawn storm. may not be the best in all circumstances but a plan is better than no plan. if you don't like this idea then try to get your bishops, knights and queens aiming (if your opponent castles kingside) at the h2/h7 g2/g7 squares and after a few goes at this idea you could find sacrifices that commonly appear. in short pattern recognition.

if you can't find any way to attack then get a good pawn structure and find tactics that damage your opponents pawn structure. exchange pieces and ultimately get a better endgame and win that way.

Quite tricky with the opposite bishops even though you had 2 extra pawns. You allowed your Ra8 to be trapped by the bishop obviously so perhaps 21.Qd6 aiming to play a6 and b5. I think your queen belonged on d6 - a dark square it cannot be removed from.

You should be looking for imbalances: where you are strong and weak.  Note that, at the move 20 you mention, that your strength is the dark squares and your weakness the light squares because you have a Bishop that moves on dark squares while your opponent's B moves on the light squares. Yet, on move 21 you trapped your own rook on a light square.  You moved your Q onto light squares on moves 22, 23, and 24. All the while notice that EVERY one of your opponent's Pieces and Pawns are on light squares so that even though your Bishop is in the middle of the board, it's not attacking a single enemy piece.

Now look for the imbalances.  The Queen-side is fairly equal and all your Pawns and your Bishop are on dark squares. As long as you can defend a7, White can't do anything to you on the Queen-side.

You have a pawn majority on the King-side. THAT is where you have to make your attack. Moving your King to h8 was not a bad idea.  Notice that White's d-Pawn makes its hard for his Bishop to do anything on the King-side of the Board. One possibility: You could have considered ...e5, which makes your e-Pawn no longer a target with the idea of using it as a hinge and pushing your f and maybe g pawns.  If you can get your e-Pawn to e4 with your f-Pawn on f5, you can force a Passed Pawn if you can compete with White's Major Pieces for control of the e-file. After ...e5 ...Qe2 then ...f5 you will capture the White Rook if the e-file Q and R haven't moved - the threat might weaken White's e-file control.

That is off the top of my head but surely a King-side attack of some kind, emphasizing dark squares as much as possible and giving yourself a Passed Pawn and using it to limit White's ability to maneuver, should win the game.

21... Rfb8 just looks misguided to me. My instant reaction is to play 21... e5 instead, with the idea of pushing the f-pawn.

There is no risk of white trapping your bishop with something like Rb3 and c3, since black can play f5, f4, and then the bishop can simply go to e3 if necessary.

Ditto to all the above comments. Let's assume you went wrong after move 20, so let's do an assessment of the position after your 20th move. In general, consider imbalances in: material, development, mobility, space, pawn structure, pawn balance, pawn weaknesses, pawn advancement, king placement, bishop colors, piece coordination, king safety, open files, alignments, important squares, weak squares, etc.

First, the big picture--strategy: Regarding material, you're two pawns ahead, so "all" you have to do is to keep trading down until you reach an endgame two pawns ahead, then win by promoting one or both of them. One catch, as Strangemover said, is that it's a tricky position because of the opposite-colored bishops, which will make it impossible to trade off the bishops in a straightforward manner, and it's possible White could still draw two pawns down if the only pieces left at the end are opposite-colored bishops. Another catch is that after winning material you usually have to go on the defensive for a while, which is what you have here. That's just the gambit principle of the material-position tradeoff.

Second, the smaller picture--tactics. The first thing to check is if your opponent has any threats. If so, those must be parried before planning how to win. White does have a serious tactical threat at move 20: Rxe6 ...fxe6 Bxe6+, winning your queen by fork, which it looks like you saw. Your defense was 20...Kh8, which escapes the potential check. I don't know if that's the best, but let's assume it is since I couldn't find any better move.

This position interested me enough that I played it against the computer on this site at levels 5, 6, and 7 (with plenty of takebacks ) to see if and how I could win it after move 20. It was a real struggle as the levels increased! Black has a lot of positional problems: White has the initiative and is two pieces ahead in development, Black needs to develop his two rooks, Black's king is far-removed in the corner, White's bishop is bearing down on the important e8-square, Black can't advance his queenside pawns, Black has no pieces outside the pawn chain, and if Black did advance his e- and f-pawns, then White's bishop would aim at the g8-square, preventing Black's king from migrating toward the center for a long time.

With all this in mind, here is how I won the games after move 20:

Here's the FEN, in case anybody else wants to try:

r4r1k/p2q1ppp/1p2p3/2p5/2BbR3/3P4/P1P1Q1PP/1R5K w - - 0 1

P.S.--I refrained from ...e5 because I thought c3 would trap Black's bishop, but from what others have said, that's not a danger, so I'd have to look at that again. If that's true then ...e5 should win even faster.