Since weíre on the subject of faces and if itís important to you:
The single most common post-processing adjustment I perform is fixing dark rings under the eyes. I donít know if itís sleep depravation or hereditary but resting-up for the convention wouldnít hurt.
Moisten your lips. Carry a moisturizing stick (especially during the summer months).
On the subject of moister, stay hydrated. The heat will just drain you and it will show in your face so keep water or sports drinks (watch out with some of the dyes unless a blue tongue fits your character) handy.
If you can swing-it carry some blotting sheets if you tend to have oily skin. It can be fixed in Photoshop but most photographers donít bother. If you can carry a small mirror that will also help make sure everything is as it should be.
After the shot, ask to look at the picture. Donít worry if itís a little dark or bright thatís easily fixed but look at yourself and how the overall composition looks AND REALLY LOOK AT IT! This is your opportunity to collaborate with the photographer so step-up and take the time to look at what might be posted for all the world to see. If it doesnít look right to you then ask for a do-over. I canít speak for all photographers but imo any photographer worth his/her salt will only want to present the best shot(s).