Reading is a great way to learn Spanish, but it can be hard to find suitable books to get started. One approach is to find books you are already familiar with in English. That way you have a good idea of the level of difficulty, and of the general plot of the book which makes it easier. I always felt that I wanted to read real Spanish books, rather than translations, but I have to say that to begin with it is easier to stick to familar authors. Popular choices are favourite children's books, especially those like Harry Potter which appeal to adults as well. The advantage of these is that they are written in easier language and are often shorter (not the later Harry Potter books though). When you start to read in Spanish it will be a slow process, so a shorter book makes it easier to stay motivated until the end.
That said, there is a wealth of Spanish literature out there, some of it very good. I find it an incredibly rewarding experience to read a Spanish novel in its original language. Starting tomorrow I plan to write an occasional series of reviews of Spanish novels to help pick out some good ones for Spanish learners of different levels.
One last tip - try not to use the dictionary too much when reading - it makes for a slow and frustrating experience. It is not essential to understand every word, as long as you can get the gist. I only look up a word if it is key to the meaning of a sentence, or if it appears several times.