When thinking about where in your home you should place a scratching post for your cat, keep in mind that it must be somewhere they like spending their time. It should also be somewhere that is convenient for you, so that the scratching post doesn't get in the way and create a disturbance. Avoid placing it near anything of value that can easily be broken.
If you have big cats, you should fasten the scratching post to the wall and nail it down, so that it doesn't fall over when they jump off it. If your cat likes to look out the window, they would love to have their scratching post placed close to one. This way they can lie down and relax, while keeping an eye on what's happening outside.