In case anyone missed the announcement on the Stack Overflow Blog, the moderator elections are scheduled to begin on the 14th February.
The election process
The best way to get an idea of the election process is to check out another SE site. For example, here's the election page for the programmers SE site.
What does a moderator do?
There's some general guidance on being a moderator at the top of the programmers election page. If you already visit the site almost every day, answer, edit and re-tag questions as appropriate, participate in meta when necessary, and vote to close/delete, then being a moderator will involve little extra work.
This site has never -- touch wood -- had a problem with difficult users. We get the occasional SPAM message, but even that's fairly rare.
Others mods - feel free to add or edit this post.