Corinda's 13 steps to mentalism is getting on in its years, but there is plenty of usable stuff in there, a lot of it tends to suit the old medium style presentation, as opposed to what mentalism currently is. But it will also give you an excellent idea of what getting into mentalism is like, and the basis of most general modern techniques used in mentalism.
You'll get a whole lot of people here telling you that you don't know what its like to get into mentalism, and how difficult it is, they aren't wrong, and 13 steps will show you very well.
Wait till Craig Browning posts in this thread, then do exactly as he says.
Since you posted this in the Card Magic forum, and not general, are you meaning to get into real mentalism? Or mental magic? The difference being something like Cold Reading for example, or presenting Out Of This World as the power of the subconscious? Both are quite different.