Noppharat Thara beach is about a 15-20 minute walk from Ao Nang. It's a long stretch of beach The northern end past the canal and ferry pier is even more secluded area where at low tide it is possible to cross to a selection of 'islands'.
The pier at Noppharat Thara is where you'll need to go to pick up the Ao Nang Princess to Phi Phi Don.