Lip liners are certainly very effective in giving shape and definition to your lips; they can add volume to your pout and make sure that your lip make up stays intact for a longer time.
However there are things that you should watch out for when you put on your lip liner:
Match the shade: For a while there, the Fashionistas had informed us that it was cool to use a different color lipstick and a different color lip liner. However that contrasting look was never really appealing, so make sure that the color of your lipstick and lip liner or lip pencil is as similar as possible.
Make a thin even line and Blend: Make sure that you don’t apply your lip liner with a heavy hand. Remember it is for outlining and not filling. So a thin precise line that follows the lines of your lips should be applied.
Then when you fill in the rest with the actual lipstick or lip color make sure that the two elements blend and look even and uniform. Often times your lipstick will wear off and if not well blended, all that you will be left with is the lip liner, which is not going to look good!