first of all, choose a picture with a clear background: it will be easier to work on it.
crop your icon as you like; i suggest you to leave some negative space above the head of your subject
add a new fill layer with the color you prefer (try to play with different colors and choose the one that looks the best on your icon :)) and set this layer to 'multiply'
duplicate your base and drag it to the top
edit -> transform -> 180°
erase the background of your picture (usually, I use the eraser with the layer mask, but you can choose the magic eraser or the pen tool)
edit -> trasform -> free transform
reduce the width and the height of your picture until you get a nice composition, then drag you subject to the top left/right corner of your icon
again, add a new fill layer with another color you like (it doesn't matter how the background picture looks, we're gonna fix it later)
with the last color fill layer selected on your layer window, paint the background of your picture with a small black brush. this is gonna erase the part of your fill layer that covers your base
now, add your text and you're done! i usually put it between the first and the second picture, but you can put it wherever you like :)
if you have any question, just leave a comment and i'll try to make it clear.
I absolutely don't need credits for this, but i'd love your comments!