In the United States, it is recommended that most male and female dogs be spayed at or around 6 months of age. This way, females never experience a heat cycle and males do not reach sexual maturity. However, if you have a female dog that has already experienced her first heat cycle, it's up to you to have her spayed at the right time.
Veterinarians recommend spaying before a dog's first season, but it is completely safe to spay immediately after her cycle if your dog has not already been spayed. If the dog has already gotten pregnant, you must wait until 12 weeks after she delivers her puppies to have her spayed. She will not become pregnant again in this time.
The health benefits of spaying your dog before or very soon after her first cycle include a decrease in the risk of mammary or uterine cancers. In addition, spayed female dogs generally live longer, though the cause and effect nature of this statistic is not entirely clear.
When your dog is spayed, you'll need to allow time for your dog to heal and recover from her surgery. Your veterinarian will give you specific post-op instructions for your dog, but in general, your dog will come home wearing an Elizabethan collar to prevent her from licking the incision, which could cause infection. You will need to keep your dog from jumping or running for the first few days after surgery, and your dog will need a quiet and comfortable place to rest. Check the incision site daily, and do not bathe your dog for at least a week to 10 days following her spay surgery.
Following a spay surgery, some dogs will exhibit a lessened interest in behaviors such as mounting or marking (in both males and females). Your female dog will no longer have any discharge or a heat season. Some dogs show a propensity for excess weight gain after being spayed, but a healthy diet and regular exercise can prevent this.