I have a lot of books that I have dug into. I love most of them. HA!
One thing that I have noticed about myself that it is super duper important for me to know what a character looks like. It is the first thing I do; explain what my characters look like. I grantee you, you will know what the hair color is, eye color, height, build, everything. Down to what they are wearing. From the word go, you will be able to picture them.
I am reading Water for Elephants right now. It is really good, and I'm enjoying it BUT, I'm on chapter 4 and I have no clue what the character looks like. Its a little agonizing. However, I have seen the previews for the movie so now I'm just picturing Edward Cullen! (I don't know if that's good or not)
What is important for you to have in your books?