There are very few people who can not benefit from wearing foundation when they are going to have their photo taken 234094 times (estimation approximate). Applying the basics to men is much the same as applying it to women. Actually, pretty much exactly the same.
Have them wash their face and moisturize if necessary. Then, primer, foundation, and concealer if necessary. Put setting powder over it all and instant improvement for photos! The bonus of this is that it's basically idiot proof, too. Apply primer, rub over face. Apply foundation, blend out. Apply concealer, blend out. Dust powder over face. You can even use (clean) fingers for everything but the powder if you don't want to invest in brushes or sponges.
If you want to get fancy, you might look into tight lining their eyes and contouring their faces. Youtube is full of tutorials to browse until you find one that works for them. Nude, matte eyeshadows are good for some eye emphasis, but experiment before the con to find out what looks best.