That's great advice. Most people don't realize that building muscle is a defense mechanism. You have to push your muscles to failure if you want to see results. 12-15 rep range is great. I personally go with a 8-12 rep range because I want to try my best to stimulate only the Type 2 muscle fibers but my goals are probably a little different. The key is definitely to always go to failure. If you can do another rep, do it. Go until you can't go any further during a set and it will ensure that you cause the most microtears and therefore the most overcompensation you can.