Hi Sabri,
Thanks for the great question! This is a popular one. Okay, first things first. Liquid eyeliner is one of the trickiest things to master in make up, so the number one thing you need is good eyeliner. My number one recommendation by leaps and bounds is Lancome Artliner. You can find it at Lancome.com or most department stores.
It is available in 11 shades, which is great. It has a pointed felt tip, that never drips which is perfect for application. Elle and freebubbles have some good tips. If you want a more dramatic look and want to make it easier on yourself, draw a line with a kohl liner first. Use a kohl liner because it goes on very smooth. Propping the elbow is also good if you are shaky, and if you apply your make up seated.
Other than that, practice, practice, practice. I do not use one stroke. It leaves too much margin for error. I start around the middle of my eye, with eyes closed. I visualize how I want the line to look and draw out, then I start at the inner corner and draw a line to meet in the middle. I find this makes it so much easier.
One last thing, Never pull one the eye. You will cause wrinkles.
Let me know how you make out.