Are you doing a pencil, gel, or liquid? All of them have their own challenges. Some pencils are better than others, but I also haven't used a pencil in a long time. Ones where I had to press down harder and were dry were trash to me.
I like liquid with a brush, but I had to stop because my oily lids would just... Melt it off. I could get some crisp lines with them, though.
For gel, I would use an angle brush. I would start from the center of the eye outwards, then go from the outside to the middle to even it out if that makes sense. After I did that, which I always find to be the least forgiving part, I would do the rest of the eye.
No matter what type I am applying, I would have a mirror near my face, my elbow on the table, and the brush or pencil in my hand. This way, I only have to control my hand with my wrist. I don't have to think about my shoulder.
Make sure you have some good, gentle makeup remover. Practice a LOT. I also just had to wear it for a bit just so I get used to my face looking different.
I found that using a lighter hand on the lower part of the eye, if I put any, gives me a look I prefer over lining the whole eye uniformly.