First (or last, doesn't really matter when you do this) remove the neckline hem (already gone in this picture). It's not important to cut perfectly straight as the edges will curl a bit anyway, looking fine even if you slightly mess things up.
Next: cut off the sleeves in a rounded line, like in the picture. Cut off more in the back than in the front, for that tank top silhouette.
It's pretty clear in this picture. Protip: cut off LESS than you would for a perfect fit, as the edges curl in (as you can also see in this picture), exposing more skin than you would expect.
Now, since the top was a bit too bare in the front for my liking, I wanted to pull the fabric back a bit. I figured I could do this by tying the back part of my tank top together. This would also add a bit of easy detail: double win!
I started by cutting off the hem of one of the sleeves.
Gone! After that, I just wrapped the piece of fabric around the back of my tank top few times and tied it in place. You can also get your needle and thread out to get a nicer finish, but the knot was perfectly fine for me.
EASYPEASY, and the perfect way to update all of your oversized, boring or ill-fitting t-shirts.
You can cut away less fabric if you don't want to show your entire bra of course, but I like the look. CLASSEH. Hope this helped!