I’ve used pencil, liquid, ones where you apply with a little brush, and mechanical pencil.
My top fave is the mechanical pencil. For some reason I find they apply easier and smoother, and you don’t have to sharpen it. Next is the ones that comes with a little brush, I use the straight edge of the brush (like a knife edge) to apply a thin line.
Apply the eyeliner straight on, and it helps if you have a magnifying make up mirror.
Like others have said, practice practice and more practice. I’m far from perfect, but comparing to when I first started to now, it is way better. And it does take a steady hand.