To apply liquid eyeliner, line the eye from the inside of the lashes outward in one big sweep. You can also line the eye from the middle of the lash line outward, then finish the line from the inner corner of the eye to the middle.
Here is another trick:
-Start with a completely bare eye.
-On the upper lashes, dot the liquid liner into the spaces between the lashes, wiggling the liner into the lashes. The result is not supposed to be a line. It's supposed to look as if the lashes themselves are super thick at the root.