Foundation is the, well, foundation of your makeup routine, and it's also the step most prone to pitfalls.

Here are the biggest foundation mistakes and how to avoid them.

Picking the wrong color. This is the biggest mistake you can make, so we'll start here. If your foundation doesn't match your skin color, you'll end up with a line of demarcation where your makeup meets your neck — not cute on anyone. The best solution, of course, is to get a good match. Test foundation colors on your face, not on your hand or wrist. Put some product on your cheek, your jawline, and your chin. Now, walk around like that for about an hour. I know, that sounds (and looks) crazy. But many makeup products oxidize — that is, they turn a shade or two darker when exposed to the air, much like apples do when cut. You want foundation that still matches your face after 60 minutes.

Picking the wrong formula. The wrong foundation formula for your skin type will only emphasize things you might be trying to hide. If you have dry skin, a matte foundation will make it look 10 times drier. A dewy formula will make oil-prone skin look like an oil slick. Not sure of your skin type? Stick with a demi-matte finish, like the Urban Decay Naked Skin Weightless Ultra Definition Liquid Foundation, $40 at Sephora.

Picking the wrong coverage level. Foundations vary, from sheer to very full coverage. Those full-coverage foundations are amazing if you're trying to cover a scar, intense acne, or hyperpigmentation. If you don't have those concerns, a really full-coverage foundation can look too heavy, even leading to the dreaded cake face. (You know the look — so much makeup that the person looks as though she's stuck her face into a bag of flour. Eek.) On the opposite end of the spectrum, a really sheer formula may not offer you enough coverage, letting skin issues peek through that you'd rather keep hidden.

Not blending. The No. 1 cause of streaky foundation is not blending the product well enough. I recommend using a brush (try the up & up Complexion Brush, $6.99 at Target) or a beauty sponge (try the Real Techniques Miracle Complexion Sponge, $6.99 at drugstores), rather than your fingers, which can smear the foundation around rather than blending it. Use small circular motions to blend the product into the skin. Make sure to cover your whole face — unmade-up areas will become very apparent as the foundation oxidizes.

Alison Smith likes to keep full- and sheer-coverage foundations on hand for different occasions. Got a burning beauty question? Email