A simple four-letter word is one of the most common pieces of advice given to new writers. Read. Read everything you can get your hands on. Read a lot. Pay attention to what works and what doesn't. For tips on being an observant reader, check out this article at Writer's Digest.
The only hard and fast rule for reading is you can't stop doing it. Some writers read only when they're letting a WIP rest. Others read daily and the rest fall somewhere in between. I've set aside one day each week as a reading day. What about you? How often do you read?