How to know if your pacing is too fast/slow
Question: When writing, I feel like the pacing is fine. However, when I reread or go to edit, I either feel like things are too slow and unexciting or too fast so that the information can't be taken in. When I ask other people to read it, they say the pacing is just right.
Is there any way you can evaluate the pacing of your own writing without using the method of waiting a couple months and then coming back?
Answer: If you're getting positive feedback about pacing from other people, especially people who are avid readers, you must be doing something right. It can also be a good sign if the pacing feels right while you're writing or re-reading your words (though that depends on how good your instincts are, which is why you need other people's opinions for confirmation).
Good pacing is all about variety. You want some slow moments or moments where the emotional tensity is turned down a notch because they allow the reader to rest and take a breathe in between the faster, more intense moments - which are also important because they keep the reader interested. You want some moments where the character reflects on things and moments when he/she is caught up in the action. Scenes can alternate with exposition. And you want to switch emotional tones regularly. For instance, scenes of anger, fear, jealousy or sadness can alternate with scenes that are light-hearted, romantic, or comic. Events the main character feels good about should alternate with negative developments - or developments that go in a different direction entirely. (Of course, this variety must be appropriate to your story and genre. Not every book needs comedy.)
The important thing is that you don't stay on one note for too long. For instance, rather than three intense scenes followed by three slow-paced scenes, you might be better to alternate between the two. Keeping things intense for too long can tire the reader out, while too long a rest period can start to bore the reader.
If you're really in doubt (which I'm not sure you should be since you're getting positive comments), try going through your manuscript and identifying each section according to whether it is fast/intense or slow/subdued, whether it's reflection or action, scene or exposition, main plot or subplot, and what the emotional tone is. See if there are places where you stay on one note for an extended period and whether it makes sense to break those up.