Maybe you've just pulled on some new pants. Maybe the hem on a pair of trusty trousers has simply ripped. There are a number of reasons why the pants you want to wear right now are a bit too long, but you're just three steps from pants that fit.
Then fold the cuff of one leg under until it's at the desired length. Ideally, the hem of the fabric should just touch the top of your shoe. Stand up and take a look in the mirror. Look okay?
Double-sided is preferred, but regular can be used as well. Secure the fold in the front, back and, if necessary, two sides.
While minding the tape, replicate the folds and taping on the other leg. Run a medium-heat iron over the edge of the fold to create a crease for the cuff, while helping the tape bond to the fabric better.