Looking good for your session is fairly simple. Make sure you choose something classic that won't be outdated in a few years. Consider what room your portrait will be displayed in and pick colors that might go well with that room.
Make sure your clothing fits well. Color and style is one of your most important decisions. Pick colors that compliment you. Families can choose a few colors and mix them into everyone's wardrobe. Make sure your clothing is wrinkle free. Wrinkles will show and become a focal point.
Avoid sunburns. Make sure your nails look neat. If you normally do not wear make up, possibly consider a little lip gloss and light mascara. They can bring a slight contrast to those important features.
If you have questions please feel free to call me. I want your session to be as memorable as possible and would be glad to help in anyway I can.