Don't rush things. Make the book detailed, but not too detailed to where the readers skip over a bunch of stuff. Spellcheck is a must. Punctuation. Watch how you end chapters. There's a difference between a cliff hanger, and something that makes it seem like you cut part of the chapter off. For instance:
"There was a knock at the door. I opened it, and it was..." Don't. EVER. Do that. Okay? EVER!!! I'm serious. Never do it. If a chapter ends like that, I automatically don't read the rest. Try to incorporate your feelings into the book. Like, how you would feel in the situation your character is in.