I'm taking a t-shirt, in this case one from the JQuery Oxford event in 2012 that I've never worn because it's too baggy, and taking it in at the sides to give a more form-fitting and flattering shape.
To do this I'm setting it up on a tailor's dummy and pinning it to the shape I want it to be, then using my overlocker to remove the excess fabric and create side seams.
This project is easier with a tailor's dummy and an overlocker, but there is no reason you can't have a careful friend do the pinning while you are wearing the t-shirt, and also no reason why you can't use a conventional sewing machine and cut manually if you find another way to finish the cut edges.