They should be snug, but not so tight that they cut off circulation. Wear diving booties or reef booties with heavy, stiff rubber diving fins. Wear a thin sock with softer rubber swimming fins. Lube the inside edges of the fin with petroleum jelly. Apply anti-chafing or blister pads to previously affected areas you can buy them at any drugstore.
Rinse fins with fresh water after use.
Store fins at room temperature and out of direct sunlight to prevent deterioration of the rubber. Test fins in the water prior to purchasing them, if you have that option. Fins will feel much different when wet and in use than they will on dry feet in a store. Snorkeling is an inherently dangerous activity that can result in serious injury or death. We recommend that you seek proper training and equipment before attempting this activity.