There are two good ways that you can learn dovahzul. You can either learn from the sites Learn section here...

http://www.thuum.org/learn/

Or there is a Memrise course for it as well.

http://www.memrise.com/course/10050/dovahzul-the-dragon-language/

If you have any furthur questions or need help, feel free to ask!

Mirkrilaar has spoken true, but let it be known that there are two better Memrise courses being made, and those will be the best way to learn when they are released. Keep an eye on the front page for them!