I have really poor conversational skills and I want to improve them. Is there any books, methods, practices or products you recommend, or that helped you in he past?

Nothing I can recommend, really.. But I'm a naturally good conversationalist, and I would say there are a few "easy" things you can do to improve your ability to hold a conversation.

Just like working out improves your physique, reading and interacting with like-minded (and preferably intelligent) people will flex your conversation muscles.

Reading gives you material to talk about. Read a lot of interesting books. Try to stay away from fiction. As much as I love fiction, it doesn't provide a lot of interesting topics of conversation.

Also, simply going out and doing interesting things gives you topics to focus on. Try to stick with things that YOU personally are interested in. This way when you talk about these things you feel comfortable, and confident.

eg. If you like rock climbing, explaining to a woman how rock climbing makes you feel inside is a way to build rapport.