I have been through a few youtube videos and other tutorials elsewhere to find out how to create those really crisp and clean outlines when drawing or tracing sketches in Photoshop. I am using a Wacom Intuos 3, with a sheet of paper pasted on top to make the pen feel more natural (it works great, by the way) and I do consider my stroke pretty confident and my hand quite steady. But to follow/trace the curve of the underlying sketch and make it look elegant and effortless – it is a bitch! Actually it is a no-can-do – for me, at least. For this example I took my “babe in the sexy outfit” image

I opened the image in Photoshop, copied the background layer (CTR + J on PC or CMD + J on Mac), created one more layer on top of the copied one (CTR/CMD+SHIFT+(ALT)+N = hold ALT if you do not want a NEW LAYER dialog box to appear, otherwise, use the same combination without ALT so you will be able to name the layer on the go, which is a good practice) and filled the layer with white colour.
There’s is a very nifty keyboard shortcut for filling the layer with background or foreground color: just make sure your background and foreground colors are set to default by either clicking the two overlapping black and white squares near the bottom of the tools palette(see image) or simply hitting D on your keyboard. From then, just CTR/CMD + BACKSPACE to fill the layer with white or ALT + BACKSPACE to fill it with black. For the purpose of this example, white is recommended;)

- setting default colors in photoshop
Then, I changed the white layer’s opacity to the point where the original sketch showed through but remained nicely dimmed allowing my new, perfectly crisp and clean lines to stand out. In my case this is around 70% and you can either do it dragging the opacity slider (located in the top corner of the layers palette) down to 70% or simply hitting the number 7 on your keyboard (if you type 7 quickly followed by 5, the opacity will change to 75%).

- changing the opacity
After that, all I needed to do is to create one more layer on top of the white one(again CTRL/CMD+ALT+SHIFT+N) to put my line-art on and I was all set for the hard work.
First of all I tried to go on about it “traditionally”, with the wacom and the brush tool tracing the lines free-hand, erasing unnecessary bits.
When you do that it is important that you first pick a basic round, hard brush(opacity 100%, hardness 100%), open up your BRUSHES palette (F5 on your keyboard or WINDOW > BRUSHES) and make sure you only tick the SHAPE DYNAMICS box changing the SIZE JITTER to PEN PRESSURE

- brush dynamics settings
However good this technique might be for some people, I had to give up. After a couple of hours of drawing, erasing, redrawing, erasing again I had this and was nowhere near satisfied with the result:
Worn out and disappointed I decided on the pen tool (P on your keyboard)

pen tool in the toolbox
To be able to use pen tool efficiently, It’s options for it as follows:
Here are first results:
TO BE CONTINUED…