Makeup should be used to enhance your features, not to hide or cover up your face. Too much makeup is probably the most common beauty blunder that women make.
Match your foundation to your skin color. Don't use foundation to darken or lighten your skin, use a bronzer or blush for that. Apply foundation small amounts at a time and blend thoroughly.
Only a light dusting of powder is needed to set your foundation, whether you use a loose powder or a pressed powder. Don't re-apply more and more powder throughout the day or your face will look into a cake-y. If you get oily throughout the day, try blotting tissues.
Too much mascara will flake and become clumpy. Apply a coat of mascara, let it dry a few seconds and then apply a second coat. Do not apply more than that. Clean up any mascara errors by using liquid makeup remover on a Q-Tip. Use a lash comb or separator to separate your lashes.
Thick, dark eyeliner will look overdone, especially in the daytime. Apply only a thin line near the lash base and smudge slightly to create a soft look. Do not wear black eyeliner with dark eyeshadow, unless you are going out for the night or creating hte smokey eye look.
Dark lip liner only works if you're wearing dark lipstick. Otherwise, it leaves you with an obvious ring-around-the-lips. It can also accentuate fine lines around the mouth.