Hydrate, hydrate, hydrate
Your skin is pretty much screaming for help if you've been sick (hello, dehydration), so make sure to slather on the moisturizer and go with a hydrating foundation that will make your skin look awesome AKA not like you just rubbed it down with some chalk.
Neutrogena Hydro Boost Gel, $19; Neutrogena.com and Bobbi Brown Moisture Rich Foundation, $48; bobbibrowncosmetics.com