I'm sure you have a few t-shirts folded somewhere that are just too big. You like the design on the front, but can't bring yourself to put them on, unless your going to paint or do something dirty. Here is how to make the shirt into a fitted tee, without too much hassle.
Put the shirt on inside out. Stand in front of a mirror with some safety pins. Now pin...
Start with the shoulders, pin where you want the seam to be
Next pin under your arms, not too snug but not too loose
Pin each side. I started at my armpit on my right side with one pin, then moved to the left side. I didn't want the shirt to be uneven, or pulled too much to one side. Work in a zig-zag motion pinning one side and then the next.
Take off shirt and mark the shirt.
Cut. Add a little on the sides and armpits for a seam allowance.
It is easier to take it in than to wish you had more room.
Lay shirt out flat and pin sleeve to armhole, right sides together. Sew just the sleeve.
With sleeve sewn, put right sides together and pin some more. Sew.
Try on. This one is a little tight. Next time I will do the sleeves differently.