Premium quality pet food & fresh water at all times. Spay & neuter pets that get spayed & neutered. Plenty of toys, exercise and attention. Comfortable, clean place to sleep. If a caged pet, keep cage clean. Vet care, vet care, vet care. Training, keep them safe & lots & lots of love.
By feeding them, playing with them, walking them, giving them treats, loving them and getting them proper and complete medical care to name a few items.
If you have any specific questions post them as well as asking your vet. They are your best resource for proper care of an animal.