For example: Let's say in one particular chapter you write two scenes, A & B.
Scene A: A man goes to the doctor and browses a magazine while waiting. A picture in the magazine reminds him of his high school sweetheart.
Scene B: Flash to the memory of the high school sweetheart. She was his first love... and she died in a car accident. It's a very moving scene and gives a lot of insight into the man - who happens to now be a commitment-phobe.The chapter ends. At the start of the next chapter, the man is no longer in the doctor's office.
Keep Scene B, it's important.
Scratch Scene A, because NOTHING happened in it. Yes, the magazine he picked up while there is what reminded him of the sweetheart, but that could happen anywhere. So cut it and just stick with the flashback.
If you come across a scene that doesn't serve to move your story forward, creating (or adding to) tension and/or developing character, then that scene doesn't really have a purpose in your story. Use the chainsaw on it and move on :-)
Another really great peice of advice was to create a "deleted scenes" file. Mine is about 22 pages long so far (and growing). Not only is it beneficial in case I ever decide to recreate the scenes by adding something more important to them, but it also made cutting the scenes SO much easier! The text I slaved over won't be lost forever - just put on hold until I take the time to make it into something better (either for the project I took it from, or for something down the road).
Sometimes scenes are written to aid readers in following the story. These scenes spell things out - and often give information that the reader should already have picked up on. I'm pretty sure that this is what makes certain scenes so boring! It's like giving a reader a GPS for your story. They go on autopilot, which may seem convenient at first, but in doing so - the reader misses miss out on the beautiful ride along the way (AND they definitely don't get to make the wrong turns, here and there, that would ultimately have made the route more memorable).
If you're unsure of which scenes move your story forward, try this: map out each scene and attach a note to each one describing the purpose of the scene. If you can't think of a purpose - or if it's something that could easily happen in a different, more important scene - cut the scene.
This is a small part of writing more concisely, which I plan to post more about in upcoming weeks.