It seems each year flea season starts earlier and earlier. It is much easier to prevent infestation than to treat it, so start as early as possible. Make sure the liquid is absorbed into the skin and not wicked away by the hair. If your dog has long hair, ask the vet to shave a tiny spot so the product can be absorbed quickly. Never rub it in, or the dog will not receive the whole dose.
H eat cycles.
Get those females spayed before their first cycle. It is healthier for them, it is an easier surgery, and it results in a faster recovery. Neutering before six months of age prevents many behavioral problems.