Training my cat

How can I stop my cat doing things I don't want him to do?
The first thing to say is, NEVER smack or punish your cat. That is cruel and has no effect whatsoever. The cat won't understand what he is being punished for.
I knew someone who was determined to stop her cat from going on the bed to sleep. Her method of doing this was to smack the cat every time she found him on the bed. This made the cat very wary of her, but he knew he could go on the bed whenever she wasn't around. There is NO WAY he would be able to know why he was being smacked and he certainly wouldn't connect it with the bed.
The best way to stop cats doing something you don't want them to do is by indirect or remote punishment. The cat associates the experience with what he is doing and not with you. Statistics from animal behaviourists show this produces the most effective results. A high-powered water-pistol is very effective. So if your cat climbs the curtains he gets shot with water. If he jumps on the kitchen counter he gets shot with water. If he scratches your best furniture he gets shot with water. Don't shout, just shoot. That way he will associate the experience with what he is doing, not with you.