Sweaters, sweatshirts and hoodies with stretchy bottom really tend to ride up when you move around and settle closer to your waist. One of the first-hand solutions anyone can possibly come up with is to tuck it in.
However, hoodies are not meant to be tucked in. So, you can try to experiment hoodies with other garments. You can wear it on top of a shirt or dress longer than its length. Doing this will lessen your worries of it riding up every time you move.
You can also take advantage of items designed to keep certain clothing pulled down and firmly in place.
There's shirt stay - a device that uses elastic tension to keep your dress shirt tucked in and tight against your body. The shirt stay attaches to your socks or around your foot and then is attached to the bottom of your dress shirt; the elastic will pull both ends and will pull any extra shirt fabric inside your pants.
You might also have heard of Magnetuck - it keeps your undershirt from riding up above your waistline and help keep your pants from sagging.