Elementary Greek Grammar

In terms of the most comprehensive books for starting off with Ancient Greek grammar, I must first recommend Smyth's Greek Grammar. For many classicists, this text is the be all and end all of Greek grammar. It contains chapters on noun declensions, grammar structures, and, everyone's favorite, particles, among many other things. However, if you are looking for something slightly more accessible, I can also recommend Hansen and Quinn's Greek An Intensive Course. I studied with this book my first year of college level Greek and found it very useful and well organized.