Making the jeans layer active, I used the retouch tool set for Darken RGB with these settings.

And added some shading to the jeans

And then using retouch set for Lighten RGB with these settings.

I added some highlights on the jeans

On the layer that has the stitches, I turned the opacity down to 70 in the layers pallet.

Then using lighten and darken rgb with the same settings I added shading to the layers with the cuffs and belt loops.

I used the retouch tool with the settings above to shade this entire image so from here it will mostly be screenshots of each layer so you can see where I added the shading and highlights.

For the button on the pants I went to EFFECTS - TEXTURE EFFECTS - SCULPTURE and used the preset "silver" with the default settings.

Then used Darken and Lighten RGB on his shirt

And the feet layer, the arms layer, the ears layer and the head layer all the same way..

On the layer that has the frames and the nose layer I used the Round Inner Bevel with the default settings. Then used a gaussian blur of 2 on the nose.

And then used this inner bevel on the glasses.

On a new raster layer above the arm layer I used freehand draw to make a heart on his arm. Add anything else you would like and you are finished.