Easiest way would be to find a picture of someone else wearing the desired jersey whos body is roughly positioned close to how the "face" player is. This way the face doesn't look out of place. Also to make it look nicer, try playing with some blending options over all layers. This obviously only works if you want to switch the players jersey for an already existing jersey. To put your jersey concept (or whatever you mean by "your jersey") on the player it would take a lot more work and would be extremely difficult to make it look real. You can try double clicking the specific layer on the layers palette (More so to the right of the little rectangle becuase if you double click the left side it will try and change the layer name) this opens up blending options you can double click the stroke option and then play around with the pixel size, colour and even the opacity. Hope those were helpful guys.