The Daily Make (2014-7-22): tshirt alterations (the back, in black and white to protect the secrecy of this year’s design and colors).
I’m also doing a tshirt alteration workshop this session of camp. I made notes for the workshop while working on my tee: Try it on and assess fit (Where do you want the waist, sleeve and neck edges to fall? Where should it be snugger or looser?). Standard tshirts are made for men and need work to be flattering on ladies.
I usually cut the neckband off first, for a slightly lower neckline, but I leave the collar seam on the shirt to stabilize the edge. If you cut that seam out it instantly doubles the size of the neck hole, and the edge will need to be stabilized (you could use a hem, blanket stitch, weaving…) or it will just keep growing. I also usually make the sleeves shorter, which can be accomplished in many different ways. Be conservative about your first cut. Try it on again.