If you are at the point where you are communicating with people (via phone screen or full interviews) make sure to ask about any side projects the candidate might have. I cannot stress enough how many strong candidates I have seen with this being their leading indicator. Do not directly ask "Are you working on any technical side projects?" because they will know immediately what you are asking for and they will give you something that you want to hear. Phrase it more from the standpoint of what they do in their downtime or even what they enjoy doing other than writing code. That is where you should be able to see what kind of drive this candidate potentially has.
