If you are using pencil: Pull your eyelid taut with your finger and draw on the liner as close to your lashline as possible (make sure that your pencil is sharp so that you will get a smooth line)
If you are using liquid: Pull your eyelid taut with your finger and carefully sweep the brush as close to your eyelid as possible, creating a long, smooth line. Don't try to dot the liner between your lashes! The only way you will get perfectly lined eyes when using liquid liner is through practice, practice, practice
Tip: You might want to try to find a liquid liner marker. It makes applying liquid liner much easier because you don't have to be as careful with the brush.
If you mess up: Dip a Q-tip in some makeup remover and carefully remove the smudge.