If I don't want any stress and want eyeliner first time then this is the step I would do. Easy for anyone to do without complications.
First you want to take some sellotape and take this on your hand and place it where you want to edge of your eyeliner to be. This is the most important step because if you get this wrong the next steps wont work.
Then with your eyeliner apply this along your lash line and then follow it along the sellotape . Then from the end of the line you've just drawn you want to draw a triangle and meet up about 3 quarters along the lash line. Don't worry about the edge as the sellotape will clean this up.
Then you just peel away the sellotape and you have that clean and sharp line.