You are a rook up and your king feels draughty. His queen is loose somewhere around e6, checking from squares you have not counted, and you are spending every move looking for perpetuals instead of pushing pawns.
7 
2 
a 
g One move fixes all of it. 1.Qxe6 fxe6, and now it is a rook and the pawns on f2, g2 and h2 against a king and three pawns, which wins itself. That is simplification, and it is not a clever idea. It is the most reliable way anybody has found of turning an advantage into a point.
Trade pieces, keep pawns
The rule of thumb every coach repeats, because it is right nearly every time. Ahead in material, trade pieces and hang on to your pawns.
The reasoning is arithmetic. An extra knight with fifteen men each on the board is one piece in sixteen and hard to feel. The same knight with three men each is a third of everything you own. Pawns run the other way, because pawns are what you promote: a knight on d4 with every pawn gone cannot mate a lone king if you play it for a hundred moves.
Take the dangerous one off first
Not every trade is equally useful, so rank them by how much trouble the piece can still cause you.
The queen goes first. She is the piece that finds a perpetual from h4, or a fork on b2 that nobody saw coming, and once she is off the board those chances go with her. Then whatever is pointing at your king: a bishop on b7, a knight that keeps coming back to f5.
Do not spend three moves manoeuvring to trade a knight on a3 that is doing nothing anyway. Trades that cost time hand back exactly the initiative you were trying to put out.
The way it goes wrong
Two ways, both common. The first is trading into a draw by insufficient material: a bishop up with the last pawns swapped off on b6 is a dead draw, and so is a knight, however long you shuffle. Before the final pair comes off, count what will actually be left standing.
The second is simplifying while you are the one who is worse. A piece down, every trade makes the problem bigger, because his extra rook counts for more with each pair that leaves. Keep the queens on, keep the position untidy, and give him something to go wrong with.
If you are not sure whether a particular swap helps you, the three questions on trading pieces settle most of them in a few seconds. And know the ending you are steering into before you get there: king and queen against king is ten moves at most, and the rest of the technique lives in endgame puzzles.