Simply there is a few ways.But if the opponent is playing you must be a bit smart to finish it up.
how to win a game in few moves ?

Yeah, the easiest way to win a miniature (under 25 moves) is to play someone who is much weaker than yourself.
not entirely true, there are a lot of miniatures even among top grandmasters...
The best way to finish a game quickly, either win or lose, is to go for a crazy attacking game...

yes boring304 like this game http://www.chess.com/livechess/game.html?id=76193738

Yeah, the easiest way to win a miniature (under 25 moves) is to play someone who is much weaker than yourself.
not entirely true, there are a lot of miniatures even among top grandmasters...
The best way to finish a game quickly, either win or lose, is to go for a crazy attacking game...
To win a a chess game in few moves , this may happen By practicing Blitz and using tricks in same time it depends on the mistake of the competitor in the opening or his advanced moves

yes boring304 like this game http://www.chess.com/livechess/game.html?id=76193738
Why didn't your opponent claim a draw by repetition of moves?
how to win a game in few moves ?