The best way is by shampoo designed to kill the fleas on contact or they have flea dip. I would recommend bathing the dog with flea killing shampoo then using a flea dip which you soak a rag with after mixing and apply to the dog and then allow to dry. You have to be very aggressive in getting rid of fleas or they will only return. After the dog is dry or maybe a day later I would apply a insect repellent on the dog like frontline which lasts 30 days. Also if the dog has been in your house you want to use a flea dust in your carpets as directed on the container. If you have to vacuum be sure to throw the bag away so they do not live in your vacuum and get back out that way. Good Luck!