A caveat before I begin. Anatomical knowledge and Color Theory are beyond the scope of this tutorial. Also, I am assuming that if you create t-shirts with art from a raster program like Photoshop that you will have access to a machine that can print direct to garment from a .psd file. If you are looking to screen print t-shirts, you may want to create your artwork in a vector program like Illustrator or Corel Draw and print each layer of your art separately onto vellums for flash burning to screens. Furthermore I am not a t-shirt graphic designer, I use Photoshop for painting and drawing conceptual artwork. Add in the fact that there are a billion ways to do anything in Photoshop my techniques are probably not the best ways...

First what are you looking at? This is a technique used throughout the creation of this tutorial. Drawing with an eraser. (A)I used a 100% opacity 100% flow round brush with Shape Dynamics turned on. I paint in my rough shape and then use the same brush settings as an eraser (B) and draw with it until I have the desired shape. This can be a much faster way of making easily selectable shapes as you can just click it with the Magic Wand Tool instead of trying to wrangle that damn Lasso Tool. The shapes can be softened with an airbrush brush used as an eraser (C). *Note this last step will not be selectable with the Magic wand so make sure you are done with the shape before you erase into it with the airbrush.

When you first open a new file, click the New Layer button to create a layer to sketch on and draw your design. or if this is scanned artwork you will already have a design. :D

You can lower the Opacity of a layer by selecting the layer and adjusting the opacity in the opacity field. In this way I have lightened the drawing so that I can more easily ink it.

With the art work lightened. I (A) create a new layer. (B) Select the brush I want. (C) Turn off transfer so that there is less feathering or opacity jitter. (D) Make sure Opacity and Flow are 100% and the airbrush is unselected. (E) Set the layer to Multiply (This will allow layers underneath to show through). With my brush set up the way I think reacts most like a traditional ink brush I get to the business of inking the art (F). Notice the thicks and thins of the line it is not all one thickness. I ink rapidly and with confidence for the smoothest line possible.

Using the same brush as before and the drawing with the eraser technique mentioned above, I lay in some flat colors. Notice that I created a new layer and dragged it under the Ink Line layer.

This illustrates what I was talking about with the Magic Wand Tool. A simple click on the shape and I get a "Masked" selection...

With clean selections you can create all kinds of effects. Make new layers use a Gradient Fill Bucket (A). Play with the Opacity (B). Here I added some dimension by selecting the skin with the Magic Wand Tool and then using the Gradient Fill Bucket and dragging from bottom to top (C) and the same for the hair (D).

Here I have created a new layer just below the Ink Lines layer and set the opacity down and made the layer an Overlay layer. This has the effect of adding color to any layers below it and it also increases the saturation of the color somewhat. I grab a purple color I like and star drawing shadow shapes with the same brush I used for inking.

Similar to the shadows I make a layer for High Lights.

Here I add a little blush color on a new layer with an Airbrush brush and adjust the layer settings until it looks good to me.

And again I use a similar method for the Eye Shadow Layer.

All that is left to do now is go down to the sketch layer and poke that fucker in the eye to turn it off. Now you have a nice clean piece of artwork.

I am sorry if this was kind of rushed. It is really hard to explain things like art, it is better if you can watch a piece being created. Perhaps I will look into that in the future and post it on youtube or something and provide a link. I hope this was informative and if you have any questions I will be happy to answer them.