Proper footwear is an essential part of any successful race. The same pair of shoes isn't going to work for everyone, so you'll need to do some research. Some sporting goods or shoe stores have staff who are trained in fitting people with the right footwear for the right activity, so that's a good place to start.
As far as clothing is concerned, there are a few things to keep in mind: mobility, comfort and breathability. Make sure that your clothes don't hamper your movements or chafe. Choose fabrics that will help wick away perspiration and allow air to circulate.
Be sure to break in your shoes and clothing before race day. Otherwise, you could end up running a very uncomfortable 5 kilometers.