For at least a few days, don't do anything at all that's job-related.

Getting let go unexpectedly is usually a big shock, and your instinct will probably be to try and get back into a paying job as quickly as possible. But while you're still recovering from the surprise of losing your job, you'll make poor decisions - and poor employment decisions will make you miserable. Take a little time for yourself and decompress before jumping back in with a clear head.