Giving too much information too quickly: Whether this be too many clues, or too much about your characters, or too many characters - your readers can only process so much information that they have to retain for the 'solving' of the story so quickly. Make sure you pace out this kind of information in a manner that can be easily retained, and interesting to the reader to discover.

Having too many characters: When there are too many characters running around, the readers tend to lose track of who did what and when. Sometimes it is necessary, but other times - fewer is better. If you don't need that side character that comes in for, literally, only three pages, cut them out and see if one of the existing characters can play that role for you.

Revealing information too slowly: Yes, there is a delicate balance. Just like you can lose readers by revealing information too quickly, you can put them asleep by revealing information too slowly and dragging things out far too long.

Being 'predictable' or 'cliche': Have you ever heard the one about the detective who has this really hot secretary that he's secretly in love with? Oh, and he's always solving the case in exactly one hour on network television? Yeah, so has everyone else, so find a different schtick! Not that you would have the same one, of course, because you're writing books, but you get the idea. Whatever you're doing, make sure it's fresh and new - and add a twist (but not too many of them, because you can lose your readers that way, too).