Top affiliates answer their emails promptly. Sometimes you may get a visitor that's still a little unsure about purchasing a product. That's when they may email you with additional questions. Answer these emails courteously and in a timely manner. If you don't know the answer, either find out or forward their email to someone who can help them.
Top affiliates endorse the product.
Once again, this goes back to the all-important step of buying the product you're selling. If you truly do like the product you'll be able to write a sincere endorsement. Top affiliates experiment. Some promotion methods will just naturally work better than others. Experiment, learn from both your successes and your failures, and try to improve.