1
make a blank document in PhotoShop w/e size you want. then get the brush tool (size = varies between 3px & 5px (adjust it accordingly), tolerance = 0, hardness = 100%) and roughly draw the outline of a skull. now make a new layer bring to top then select the pentool (size = 6px) and trace over the outline of the skull you just created. go back to layer 1 (brush tooled skull) then select filter effect > plastic wrap (make everything 100% smoothness.... etc) lower the opacity of this layer to 95%.
2
now make a new layer bring it to the bottom (below all the layers) and decide on a pallette. once you have decided? apply the colors to the appropriate areas. then select the smudge tool (size = varies but about 3px min - 20px max dont touch toloance or hardness) use this tool to shift and smudge the colors you applied to the layer so as to fit with the orignal skull outline above it. finally add soft lighting via layer adjustment > photo exposure... etc. and finally add a circular gradient over the top lower opacity and soft erase to taste.
3
finished
p.s this is my first ever tutorial so i apologize if it seems very vague.