From our pal Brett Bowden of Printed Threads:

Something that I have struggled with for a long time is placement.  Where is the perfect place to start a print.  Is it 4 fingers from the collar?  Are my hands a normal size?  When struggling to decide if something is printed in a spot that will look good when wearing, sometimes you just have to put the shirt on.  I do not think that your customer would really appreciate one of the sweaty guys in the shop trying on their shirts and immediately slipping that into the box though.

I think a great way to see if prints are in a good location is to try them on a mannequin.  Uline is now carrying a lot of products for retail stores and has begun carrying these guys: http://www.uline.com/BL_455/Mannequins?keywords=mannequin

The price might scare some at first, but the cost of a rejected job is a lot higher.  Trying shirts on the mannequin is a great way to see if the pocket print is in the right place, or if the chest print is the right spot.   Noone wants a print on the belly, or a small print too close to the collar.

Obviously people come in a lot of shapes and sizes, and everyone will wear the shirt differently.  This is a really great starting place though.  Way better than guessing.