1st - keep the claws trimmed SHORT!

2nd - never hide the scratching posts. Cats scratch where they want to scent mark and they want to do that where their people are, to show that this is THEIR territory.

Have numerous posts and experiment with materials. They needent all be expensive, but they should be tall (if meant to stand vertically) and sturdy. Low ones that lay on the ground are also good. Some are cardboard, some are sisal. Even a $1 carpet sample can make a good appropriate place to scratch.

3rd - if you need a little EXRTA help, cover the favorite parts of the furniture with double sided sticky tape (they make wide strips of this that can be found at a pet store. And aluminum foil is also a good deterant.

4th - be consistant. If he goes for a no-no spot, take him to a scratching post and show him. If you are a bit too far away, a squirt of water should deter. Do it always, whenever is necessary.

if all else fails, consider soft paws nail caps.