Slouching boots come in and out of fashion, but many boots aren't designed for slouching. Still, you might find that a pair of boots goes a little baggy over time, until they eventually start bunching around your ankles. Learning how to appropriately care for your boots will help you prevent slouching.
Put the boots on carefully. Don't tug and pull on them or stress the material in any other way—try to slip your feet into them smoothly and without force. Excessive tugging will stretch the material, and over time the boots will begin to sag.
Tie or zip boots up carefully. If your boots came with laces, zips or buckles, be sure to undo them fully before putting the boots on and to do them up again properly. Fasteners on boots are designed to keep the boots in shape in addition to keeping them on your feet, so ensure you use the fasteners as they are intended.
Put paper or card in the boots when they're not in use. Don't stuff the boots tightly—use just enough paper or card for the boots to hold their shape when you're not wearing them. The ankle and calf parts of the boots need support to prevent the material from going baggy. It's best to keep hold of the stuffing that came with the boots, but any newspaper or card will do in a pinch.
Store the boots appropriately. Don't leave them under a pile of other shoes or belongings. Give them their own space, preferably enough space to lay them down flat. Boots stored upright for long periods of time will inevitably succumb to the effects of gravity.