Here's a little advice for new runners (or new runner, because I think only one person reads this blog):
1. Get a good pair of shoes. Find your local running store, and buy your first pair of running shoes there. Make sure you bring an older pair of shoes you've used for running. A competent employee will look at the wear on the bottom of your shoes as part of their evaluation. They will also watch you walk and possibly jog to see if you have any problems with rolling your feet. After all that, they should be able to show you several shoes. Expect to pay somewhere near $100. It sounds like a lot, but good shoes go a long way toward making running more enjoyable.
2. Follow a plan. I used the Cool Running Couch-to-5k plan to prepare for my first 5k. I couldn't jog a half mile when I started. Using that plan, I finished my first 5k in 32:47. The Cool Running plan won't turn you into a fast runner, but it will get you to the finish line.
3. Don't be afraid to walk during a training run. The Cool Running plan is built on intervals, and they are the key to improving your times. I'm stubborn when it comes to walking during a training run, and that has kept my improvements to a minimum. Don't be like me. (There's nothing wrong with walking during a race either, but I'm stubborn, so I don't.)
4. During your first race, don't be surprised or disappointed when you're passed by the young, the elderly, and people pushing strollers. Instead, think about how you're joining their club. Remember what it was like to run as a child. Think about how you're starting an activity that will last a lifetime. Ignore the stroller-pushers.
5. It sounds trite and cliche, but enjoy your run. Unless you're some kind of wunderkind, you're not going to win anything or finish near the top of your age group. Those people at the finish line are cheering for you though, so save a little for the end and finish strong.