Visit a few bike shops and demo a few bikes to know what size and what style of bike you want to get. Then look at craigslist/etc to find a used but good/great shape bike for a much better value than buying new. Don't buy a used dept store throwaway bike. A 10 year old trek/c-dale/giant/etc with lx/xt/sora/tiagra/105/ultegra/etc that's been hanging in someones garage and has less than 1000 miles will be just fine and you'll get much more bike for your dollar.
My $0.02
Ride it often.