Last is using the Pen Pressure option.

Pen pressure is usually used in freehand mode, making use of a pen tablet's capability to mimic your natural pen strokes.

As you can see from the image on the right, I'm not particularly good with drawing freehand with my tablet.

So, with the Brush tool again selected, I've set the Control (1) to Pen Pressure, set the brush tip to an appropriate size and angle for what I need to trace, this being the lips.

 

Minimum diameter play a bit different in this setting. Instead of 'fading' at one end, it affects the brush stroke by tapering at the ends.

Minimum diameter percentage will depend on your need, so experimentation and trial and error is inevitable when you're not used to this technique yet.

Same as before , I go and select the Pen tool (P) again , and create a path that goes from right to left using the pencils as a guide to its shape and length. Right click on the path, and select Stroke Path from the selection box.

As you may have noticed that I didn't create a path all the way towards the other side of the lips. This is because I wanted to vary the thickness of the line more, and opted to create two separate paths, which you see here.

 

Again, this is fairly trial and error technique if you are not yet used to it.

On the left you'll see all three techniques blended in to create a fairly 'natural' looking ink work.

 

I do hope that you've learned something regarding digital inking.

Now I know that this technique of mine may seem that inking with Photoshop can be a tedious and intimidating task, what with all the technical aspects of manipulating paths and brush dynamics. But once you get the feel for the tools and you start to have your own flow of shifting between them, it'll be a piece of cake.

If you'd like to ask me specific questions regarding this tutorial, or if you want me to elaborate further on any particular part of the site, you can post your questions on the forum.