the shirt is size XL, and I am a M
It depends on the style and cut of the shirt as well as the material. I've lost 40 pounds and am still losing so many of my shirts are baggy through the waist area. I turned them inside out and sewed a seam up each side about 1" from the original seam. It worked great for me.
Great pictures and directions for altering a button shirt here;
You can sew the sides to make it narrower, another trick is to leave some lower buttons undone and tie the 2 sides of the bottom together in the front.
Tie it around the waist. That should take up a lot of slack or extra material. Roll up the sleeves. Take in (on your sewing machine) what is too sloppy when you try it on.
Hi Christine, hope these help you
If you sew, you can bring the sides in a bit, and you can add darts in the back to tailor it in.... https://www.youtube.com/watch?v=DsIW5TFVGF0
I would just tie a knot in the front, it is really trendy right now!
This may help: https://thediypanda.tumblr.com/post/16122377842/how-to-turn-a-large-t-shirt-into-a-fitted-tee
Here are some great ideas. I used a big belt https://thesewingloftblog.com/100-ways-to-upcycle-your-clothing/
Where exactly is the shirt too large, - neckline, or body width, or arm length?
Taking in the side seams will help a little as far as making the width of the shirt narrower, but it won't help if the shirt is too big in the shoulders.
You will have bunching up of excess fabric under the arms unless you undo the armscye (where the sleeve is sewn into the armhole) and make alterations in the shoulder seams.