I studied Greek and Latin at school, but that was (agh-hmm) years ago now, and I've found that I've forgotten a lot. Of the books available on this site, which would you most recommend for a brush-up, rather than starting from scratch?
Try Hillard and North's Greek Prose Composition (with key). There are grammar points and an extensive vocabulary for each set of exercises. Really good. It's on the big side, but I just print out a couple of pages at a time and work through them.