A good lip liner is basically your best friend, but before you start drawing all over your mouth, or over-lining your lips, read this article and tips to find proper way to enhance your lips. Depending on the look you're going for, you can use lip liner, in combination with lipstick, to your advantage, to either enhance or minimize your lips.
Your lip liner should always complement your lipstick, not overpower it. For the best look, always aim for a liner that matches your lipstick as closely as possible. If you really want more defined line, use a shade or two darker lip liner.
If you are using a deep liner, color in the entire lip — top and bottom — then blend your lipstick all the way to the edge of the liner.
To keep things looking more natural, try to blend lip liner into fuller parts of your lips and center of your mouth instead of leaving a legit line.
When using lip liner to create fuller lips, use a neutral toned lip liner and don't go to far or try to create your own line. Remember, it's about keeping it natural, so be careful and don't extend your lip line too much, you want to enhance, not to draw attention to your imperfection.
If you want to soften the lines of your lip liner, use your finger and trace the line gently to soften it. After that use a concealer lighter than your skin tone and apply it around the very border of your lips to create a bolder look.
To prevent hard lines, roll the tip of your lip liner in the palm of your hand to warm it up.