The behavioral interview format is definitely more common now than it's ever been before. Behavioral interviews are very effective when conducted properly. Preparation for this type of interview definitely requires extra effort and time.
There are a number of great books and articles out there on the subject. Find a great book. Do a search on Google for "behavioral interviews" and look through the myriad of articles written on the subject. Read the example questions and the example answers. Reading is helpful, but this is one definitely of those areas where SKILL (practicing and doing) far outweighs KNOWLEDGE (reading about it).
The BEST way to prepare for these interviews is to practice with a third-party, to role-play and to get quality feedback. Practice and role-playing develops your SKILL and feedback reinforces your learning and helps you identify improvement ideas.
Behavioral interviews are very dialogue-oriented, supplemented with deepening levels of probing -- you're never quite sure which direction the line of questioning will flow. That is the big reason why practice works so much better for preparing for this popular interview format.
Find someone skilled in behavioral interviews with whom you can practice -- maybe someone in your network in an HR role, a friend who is a consultant in the job search field, or an outside coach. Practice is KEY to "acing" the behavioral interview.
All the best to you career success!