I have just begun working on a project which uses Mercurial as a version control system, and I need some basic tips on how to use this. Please use this question to give some
Here is a helpful tutorial on Mercurial written by Joel Spolsky.
It covers basic usage and commands, as well as how to work with Mercurial at a more conceptual level. If you are already familiar with SVN, then the first part is definitely worth reading: it talks about the major conceptual differences between SVN and Mercurial, because trying to use Mercurial in the same way that you use SVN is asking for trouble.