A simple setup will do when targeting flatfish- just make sure the sinker gets to the bottom..you may have to adjust the weight depending on the tide/current. Seaworms gathered at low tide work best although I've also had success using pieces of shrimp or squid. Hook size: 1/0-4 although i've noticed that they can swallow fairly large hooks for their mouth size. For shorefishing, which is what I do nowadays, fish during an incoming tide on a sandy/muddy bottom..If you fish off a pier in deeper water, the type of rod used may not matter so much but if you are fishing off a beach, a good shore casting rod is essential to allow you to cast your bait far enough to where the fish are located. I find that casting out and slowly retrieving the bait (with regular pauses) works better than stillfishing- you can potentially cover alot of ground by doing so (flatfish are mostly sit-and-wait predators) and the slow erratic movement of the bait may better entice the fish to strike.
I've tried boat fishing for flounder/sole years ago and I've had success with both drift-fishing and jigging techniques. You can get a good catch if you can locate "hotspots" where the fish aggregate to feed.