A slim-fitting long sleeve is ideal for sleeve scrunching because the tapered silhouette stays put against the contour of your forearms and elbow. The more snug the sleeve fit, the easier the sleeves are to scrunch and stay that way. 

Sometimes even with a relatively slim fitting sleeve the scrunch is hard to maintain because the sleeve opening is too wide with the cuff unbuttoned. One simple solution is to sew a little stitch in the middle of the placket of the sleeve. This narrows the opening of the sleeve when the cuff is unbuttoned and pulled back into a scrunched position. This makes it stay put on your arm. Snugger fit = better scrunch. 

See the photos below for one example. I didn’t have pink thread to match the shirt so I used white, which matches the textured interest in the fabric. 

I’ve used this stitch trick on a few shirts already, like my white tuxedo shirt and blue and white shirt. Some shirt styles, like the button-down shirts from Brooks Brothers, conveniently have an extra button in the position of the stitch on the placket. Those shirts also have a stiffer fabrication than most and scrunch particularly well.