These are my general guidelines for voting in RfAs. I usually follow them, but as these are just broad statements, I usually contradict them if the circumstances merit.
Total edits: 1500+ edits. The number by itself is not important, but the quality of the contributions is.
Namespace proportions: About 400 / 20% of edits should be to the Talk, Wikipedia, and Wikipedia talk namespaces, to gauge the editors ability to communicate with others.
Dedication to project: at least 3 months of active editing (active being more than 500 edits per month).
Following of policy: no blocks on the user's log in a considerable period of time, unless they were in obvious bad faith. Blocks for vandalism will cause me to almost instantaneously oppose any nomination!
Civility: Administrators are expected to be civil; any editor who does not assume good faith will usually be opposed. Newbie biters are instantaneously opposed.
Eagerness: If a user has previously requested adminship before, all the constructive criticism given during the previous RfA should be addressed. Otherwise, the editor might get an oppose from me.
Article writing: In contrast with other users, I do look at contributions to the article namespace. Featured articles and Did you knows are looked very well upon, but just decent work on a couple of articles will do. RC patrolling will not get you free adminship.
Edit summaries: I'm not too much of a fan of this editing statistic, so it usually isn't a decision in my consideration. (For the record, according to Flcelloguy's Tool, I have 99.71% edit summary usage thoughout 15,850 edits). Unless edit summary statistics are truly dismal, they will just be a comment.
Previous interactions: These usually provide the best measurement of an user's ideas, understanding of policy and civility, and they help me make a more informed decision.
RfA behavior: Campaigning for votes, harassing oppose voters, or other willful manipulation of wiki processes will disqualify editors in my view.
Desysopping: Desysopped users are usually Requests for arbitration waiting to happen, so I will apply a much tougher standard to users who have mishandled the trust given by them by the community before giving them tools they could abuse again. Prove that you've changed whatever you did before trying to get the shiny buttons back.