Mistakes to avoid when putting on eye-liner

We all know how hard it is to apply eye-liners that form one of the integral parts of your make-up kits. A lot of people think they know how to apply eye-liners but the real mess tends to begin when they notice that they really need to learn a lot out of it. If you can apply eye-liners and avoid a few common mistakes while applying them, you know you have done pretty much good a job like a professional does. What else should you want?