Visit a few bikes stores, take some out for a test ride, and see what you like. Most bikes in the same price range are specced pretty much the same. Once you have it narrowed down to a couple choices, if still unsure, you could get additional advice here. Right now, however, most of the decisions you need to make are personal preferences. The only things I would look for are the ability to run wider tires, mount a rack and fenders, and disc brakes, but these are my personal preferences, and your desires and needs may be completely different than mine.