All above are good advice. Also in my experience, my son was a good sleeper to begin, and then stated waking 2 / 3 times a night. It must have stared one night for a perfectly good reason, but it became a habbit. He then got used to me giving him lots of attention to get him back tot sleep.
The best advice for this, is to give as little attention (very hard I know) and make him understand that it is still sleep time! Don't allow him to rely on you to help him settle or the habbit will be harder to break.