It's amazing how similar plot structure is to a chess game. Like a good story, a game of chess has an opening, a middle game, and an endgame.
During the opening, players develop their pieces, protect their king, and set up future attacks, much the same way a writer sets up the story in the first act. In the first act, we meet the characters (develop our pieces), introduce the conflict (set up for future attacks), and keep turns and twists close to the chest (protect the king). A good chess player never needs to move the same piece twice, just as good writers should never revisit a scene. A good story always moves forward.
Most of the action takes place during the middle game. Pieces are exchanged, plots are devised and foiled, and traps are set. Very similar to the second act of a book. This is where we see the action as the conflict plays outs. Of course, the story would be boring if the protagonist reaches his goal unfettered, so as writers, we have to throw a lot of obstacles in his way for him to overcome, exactly like a chess game. I've played a lot of chess in my life and this all happens in a game. There are times when I think I have a plan all worked out only to see my opponent make an unexpected move and foil my plans. Or maybe I make what I think is a brilliant move only to realize I blundered (yes, that's an official chess turn). A good story has all of these elements. That's what makes for a good story. Maybe your protagonist has devised a way to overcome the conflict, only to have the antagonist make an unexpected move, or maybe she takes and action that ends up being a mistake. How dramatic and what a page turner that would be!
The game comes to a close during the endgame. After the dust has cleared, a few remaining pieces fight it out for final victory. Each player uses what he has left to bring a game to a close. Moves are made and countered, pawns (minor pieces) are pushed to the other side of the board to become queens and finally, the opponent is trapped and checkmated. How does this relate to your story? Maybe a few characters have been killed or incapacitated, or maybe you have a minor character who rises to the occasion and becomes a hero? Either way, this is where the game, and the story, ends. After the game, each player signs the score card, shakes hands with his opponent, and moves on to the next adventure, er, game.
Next time you plot a story, think about chess.