Everyone else says great things. So I'll give you general advice: read read read read read read read read!

Read every article on http://embeddedgurus.com If you don't understand something, research it. If in the explanation of those things you find something you don't understand, read some more. I'm about to head into an embedded software position and my experience is a handful of professional projects over the past few years and a lot a LOT of reading. Experience lets you try things, but reading lets you know whether the things you've tried have been done before, maybe better than you could. It introduces you to concepts that you can work with in any circumstance.

Just read!