This mistake deals with lip liner. I know it's called lip liner but it's actually not meant to be used to draw a line around your lips. Lip liner is meant to create a barrier so that your lipstick doesn't feather or travel outside of the line of your lips. Consider it a fence, keeping your lipstick from wandering away. That said, it is very important that if you use lip liner, you either blend it in onto your lips or line your lips then fill them in with the liner. This way, if your lipstick fades away, you will not have a line left around your lips that is a different color than the rest of them. In the DO photo below, I lined my lips then filled in with the lip liner before applying red lipstick.