I put this step first because it's often the first thing people do, and I want to stop you before you go wrong. This is probably the biggest mistake I made, and a mistake that I believe a lot of people who are interested in astronomy make. A lot of people think that a telescope is required to be an astronomer, and they head out to Wal Mart or Target and pick up one of those $50 telescopes they always have around Christmas time.
People who have been doing this for a while have a name for those telescopes--they call them hobby killers. Those things are incredibly difficult and frustrating to use, and aren't good for much except looking at the moon, and while that's definitely worth doing, don't take that step yet. The one I bought was awful, I used it a couple of times and then put it away, convinced I was doing something wrong. It put at least a two year break between me deciding I wanted to get into astronomy and me actually doing so.
You will probably want to get a telescope some day, but you really don't need one yet, and you most definitely don't know what kind you want. There is a wealth of options out there, and you should take some time to learn about them before you settle on one to buy (more on that in a later step).
If you absolutely must spend some money on something (I know sometimes if I drop a few bucks on a new hobby I feel obliged to see it through), buy a Planisphere
. This is a very useful resource you will come back to over and over again, and worth the few dollars it will cost.
has pointed out that another good, small investment is a green laser pointer. They are very cheap these days, and if you're planning on involving anyone else in your hobby they are great for pointing out what you're looking at. Also, they're fun!