I'd recommend using the 'pen' tool in photoshop. It takes some getting used to, but once you've figured out how it works, it gives crisp lines and is easily fixable, unlike inking in real life!
How it works:
1) Open image in photoshop.
2) Create a new layer! Work on that layer when you're 'inking' or else you won't be able to get rid of the lines!
3) Select the brush tool. Make sure the size of the brush is how thick you want your line to be.
4) Select the pen tool. Click on the point over the line drawing. Click and hold on a point further down the line, then drag the mouse/touch pad around so that the curved line matches your pencil drawing.
5) Repeat! If you want a sharp point, you have to create a new anchor point
without dragging the mouse around to create a curve... or else you get these funky not-quite-points.
6) Right click, select 'stroke path'.
-For a smooth, normal line, make sure the little box isn't set to 'simulate pressure'.
-For a line that gets thinner and fades away at the tips,
do select 'simulate pressure'!
7) Once you're done with a line, hit 'return' to delete the path.
Here's a tutorial I found while doing a quick google search.
http://acaraluv.deviantart.com/art/line ... l-21814747
Hope that helps!