Thanks for your replies guys!
Here are some more:
* Not cleaning your make-up applicators and brushes.
Applicators and brushes should be cleaned at least bi-weekly. Oil and bacteria build-up can wreak havoc. If you're prone to pimples, you'll be surprised how much this strategy works.
* Using too dark lip liner.
Don't use lip liner that is darker or lighter than your lips. When the lipstick wears off, you're left with a dark ring around your mouth. Try using lip liner that matches your lips and fill in your entire lip area.
* Leaving makeup on overnight.
We've all done this, but at what cost? Leaving make-up on for long periods of time clogs your pores and makes you more prone to blemishes. Don't do it, you'll feel better.
* Crooked, uneven liquid eyeliner.
If you choose to use liquid eyeliner, the trick is practice and a steady hand. If you can't keep your lines even, opt for an eye liner pencil.
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