Show your product to 5 people. Don’t explain it. Just watch. Ask them to talk through what they are thinking. Watch them try to figure out what your product is all about. Watch them skim, click, dismiss. Watch them ignore your new feature. Watch them try to get direct answers to basic questions. Watch them fail to see your save button (which is inexplicably suddenly more hidden than a forgotten sock left in the dryer or the lost sunglasses on the top of your head). Watch them get bored with the burden of trying to find something they actually want from your product.
When it comes to support, the same principle applies. Watch your customers. See what questions they run into. Don’t just stock out an entire help section with questions you think they might have. Find out their real questions and answer them.