This is the best book on technical interviews for places like Google:
http://www.amazon.com/Cracking-Coding-Interview-Programming-...
http://www.amazon.com/Cracking-Coding-Interview-Programming-...
Additionally, glassdoor.com has a lot of user-contributed interview questions and lets you search for/filter by specific companies.
Work through CLRS algorithms book
Practice explaining technical ideas in spoken conversation.