"Everything should be made as simple as possible, but not simpler."
“Simplicity is the ultimate sophistication.”
- Leonardo di Vinci
It seems like an obvious thing to do, but it can be hard: take out the boring parts. Nobody wants to waste their time, so reduce the length of your game, or reduce the boring aspects, so it is more fulfilling.
Step 1 is identifying what is boring. If people have no reaction to it, or it seems klunky or uninteresting to you, take it out. People will rarely say 'this part bored me'. They are more likely to say things that imply that though, such as, 'it was too long' and 'it was OK'. Watching the players and seeing where their attention is at different points really helps. Is it on the game, or out the window?
Take out annoying parts, frustrating parts, boring parts, dull parts, and overly-complicated parts. Don't be afraid to be critical, especially of your own ideas.
Read "The Elements of Style". It is a great book.