The resource I have always recommended here is How To Design Programs. This online book will take you through the basics of Scheme. Its fairly low level, so you can skim the first few chapters, but it has a ton of exercizes, so you'll get a lot of opportunities to extend the examples.
The other book I always end up recommending is The Structure and Interpretation of Computer Programs. This one leans more toward traditional computer science, but you'll definitely learn a lot if you've never read this book before.
