I am a beginning seamstress, and hardly ever do clothes, but I wanted to make some dress shirts short sleeved so that my husband can wear them to work in warm weather. Making a long sleeve shirt into a short sleeve shirt should be easy! Plus, there are lots more long sleeve shirts on clearance racks.
1) First, I ironed the shirt and made a mark where I wanted to cut the sleeve. I used a short sleeve dress shirt to decide where to mark, adding an extra 1-1.5 inches for the seam.
I found this link for making short sleeves on a woman's t-shirt.