When doing your liner it's always important to start from the outside and work your way in toward the eye. (towards your nose)
1. First make a very small line angled toward the end of your eyebrow.
2. Next connect that line to the outer corner of your eye.
3. After that you can connect that line to the inner corner of your eye and setting desired "thickness"
** the bigger the eyes you have the thicker the line you can can have. However, if you have smaller eyes, then you may wanna make your liner much thinner so it doesn't over power the shape of you eye. I have very small eyes, so sometimes I like to draw my liner in, only to about the middle of my eye and not drag it all the way in towards the corner of my eye. I think it make my eyes open up more.
Here's an example of how I do my liner.
You can achieve this look using any type of liquid or gel liner that you prefer. I personally use Mac's liquid liner in"boot black" which is a felt-tip liner that lasts FOR-EV-ER! (seriously, like almost a year)
Some may find it easier to use gel liner and for this I would recommend Maybelline's "Eye Studio." With gel liner the key is to make sure you have a very small angled brush.
I believe this liner comes with a brush but if you don't like it then here are some other examples of what you should look for.
Most importantly.. PRACTICE, PRACTICE , PRACTICE! No one ever gets it right the first time. I, myself struggle to get it perfect but the more and more you play with it, the more it will become effortless.