Wow! I was all set to post some great Halloween photos sent in by a library, but you'll have to wait until tomorrow to see them.
Marge Loch-Wouters has a great 2-part post about collection development, with a list of 12 ways you can be a bad selector. Here's Part One, here's Part Two. It's something I wish I'd had access to the first few years I was trying to figure out how to do this. Look here for some practical advice and good explanations. And the comments have even more suggestions to consider!
IFLS librarians--if you need help getting a handle on your collection (evaluating, getting a bunch weeded out and coming up with a plan for keeping on top of it, figuring out how to find gaps, etc.), please contact me!