Take good, clear pictures. The more pictures of each puppy the better.
Name each puppy. Puppies sell better with names. (Many people consider pets a family member and going to pickup "'Fluffy" sounds more appealing than going to pickup "Puppy #2".)
When you take pictures, make sure that you have good lighting.
Put as much information in your listing that you can. (Regstration type, mother's personalities, etc)
If you are aware of any issues, make them known very clearly on your ad. People don't trust people who act "shady". Nothing destroys a sale quicker than trying to downplay or minimize issues you know about.
Return phone calls and emails promptly. Don't wait a day to get back to people.
Document all medications your puppy has recieved, and if you are offering a health guarantee, (which we highly recommend) make sure the guarantee is clearly spelled out.
Check with your local laws regarding puppy sales-you want to make sure you are legal.