First thing, remember that you can always go over your lid more than once so no need to get it exactly the thickness you need on the first try.
Another tip, the more pressure you use the thicker your line will be. the less pressure the thinner.
Finally, when applying liquid liner avoid using the actual tip of the wand to place the color on your eyes, instead use the side of the brush and lay it flat against your lid and drag it across. This will give you more control and will almost guarantee you a thin line close to your lashes.
start from the middle of your eyelid, with short strokes, you don't have to make one straight line in one swipe, if you take your time and connect little lines, it's going to come out better for you. Just keep practicing, some liquid liners are easier to use than others.
To line your eyes there are a couple of different ways to go about it, as listed below:
If you don't want to actually line your eyes, but enhance your eyelashes try this technique: Starting with 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.
By the way, a very “user-friendly” liquid eyeliner pen for precise application is YSL “Easy Liner for Eyes” which gives great color payoff. You can find it at: http://sephora.com/browse/product.jhtml?id=P218205
I hope this helps you.
I always start at the outside corner of my eye first. First I pull my skin taut (so it's easier to line the curve of my lash-line). Then l use the side of the brush (not the tip) and slowly drag at an angle to line my lash-line. I do this is multiple strokes, and do a finishing stroke over the mini-strokes. It is SUPER easy to fix any mistakes with a Q-tip. If the application of the line is too thick, quickly wet a Q-tip with water and rub it over the top of the line (just enough so your barely thinning it out). I hope this helps!