I've been teaching myself to play for about 3 months now. I found chord changes difficult at first but you're right- it does come with practice.
Books I have are, Learn To Play Guitar With Metallica, and Metallica- Riff By Riff. The latter is good for learning riffs and if you're not a Metallica fan I'm sure you could get a simialr book for a different band.
At the moment, I'm learning the Enter Sandman solo, so you could try something like that.
Hope this helps and good luck.