Skip the Foundation
Especially if you have acne prone skin, using a heavy, liquid foundation can make you look very unnatural. If you need to, apply your concealer first, then use a light powder foundation or a tinted moisturizer to even out the rest of your skin tone. Using too much foundation can make you look older than you really are, so avoid that at all costs.
Pat in Concealer, Never Rub it in
When applying concealer make sure you don't apply it directly to your face, bacteria can get onto your brush and contaminate the rest of your make-up, put it on your finger and pat it on your skin, you never want to rub it in. And make sure that you get a shade that is closest to your skin color as possibly. You don't want it to be noticeable that your wearing any.
Make the Focus Your Eyes OR Your Lips, Never Both
Pick one of your features that you want to be the focal point for the day, you can switch this up day by day, but you never want to combine them. Play up that feature, you don't want to look like you just walked out of the circus when you walk into the room. And even with picking one feature, make sure you don't go overboard, the natural look is in.
And Most Importantly...
Less is More
The natural look is definitely in now. Wearing too much make-up can make you look like a clown, or like your older than you really are!