Sheltie's fur is rough. Rough fur does not require constant cleaning and washing. If fur gets dirty or muddy, most likely wash with only water will clean it up and in cases it don't then some shampoo might be required - but it's not recommended to wash it more than once or twice in half year section with shampoo.
The comb or brush should be metal-spined with long spines that are not too much but quite loose. Most of the dirt (a.k.a. mud or such) will drop off when brushing sheltie if it's dry on the coat. Fur is half-long type, and does not need trimming in meaning of trimming. Some owners or breeders cut fur from paws and clean up some ear hairs with scissors but it is not must-to-do. Male sheltie usually has more fur than female and that may require more brooming - especially then when sheltie is in epilation which usually occurs at spring and at autumn, with females epilation also occurs after litter moves from home if she has been used to breed.
Most common concerns with sheltie are: PRA, CEA and hips.
PRA (Progressive Retinal Atrophy) is recessively hereditared so the gene must come from sire and dam. There is no cure for PRA and in the end section it always blinds the dog. The PRA is usually noticed at age of 2 to 3 or at older age which is around 6 to 7. PRA-dog can live full dogs life tho, but they do not know that they are blind and so must be told to slow down a bit. The bad thing about PRA is that it can stay un-noticed for centuries in genes of the dog that it passes for future generations. Hypothetically speaking, a dam has the gene and is mated with sire with no gene, 25% of the pups has the gene but is not ill. The carrier pup is mated with geneless dog, and again 25% of the pups has the gene. This goes on, and let's say 5 to 6 generations later the carrier dog gets mated with another carrier dog 20 years after and half of the pups are sick and half carriers. The type of this PRA is older age PRA, so it is not noticed untill at age of 6 and the sick dogs get mated with health, carrier and sick dogs and when their pups have already started breeding career the PRA will be noticed and nothing can be done anymore because no-one knows from how far the gene comes and from where it can't be known for 100% that PRA wont go on unless all dogs in sick one's family will stop breeding which would cause the amount of breeding dogs go down dramatically the way there would not be dogs to breed anymore soon. PRA is one of most complicated eye-disorders with shelties.
Sheltie's original purpose have been sheepherder - due to that fact they are strongly pack animals. Their own pack is their all, they protect it, they feel need to look after it and if the pack splits up it's almost end of the world for a sheltie. That why, when you train your dog, always remember - you are the head of the pack, and sheltie is happy when you are.