The best place to start is “Fmoc Solid Phase Peptide Synthesis: A Practical Approach,” by Chan and White. Just what it says on the tin, this book sets out the principles of SPPS; from selecting from the dozens of available resins, coupling agents and amino acid derivatives to working in rarified fields like glycopeptide and phosphopeptide synthesis. If you’re just starting out, or need a handy reference text, the best section is the third chapter, which is filled with recipes and example procedures for both coupling mixes and useful indicators.
It’s easy to see solid phase peptide synthesis as a cookbook, and first few months after I started that’s all it was to me. I had been following procedures handed down from a previous graduate student and was doing fairly well, but had no idea why I was doing anything. Why was I mixing my coupling reagents several minutes before addition, and why was I using TBTU instead of HATU or TATU? 
Chan and White’s book filled in the blanks and helped me move from following procedures to (sometimes) improving them. I’ll move on to the details in the next blog post.