The main aspect of "sales" that most people tend to think about are made up of Negotiation and Marketing.
For the Negotiation aspect, you can read http://www.amazon.ca/Secrets-Power-Negotiating-Anniversary-Edition/dp/1601631391
For the Marketing aspect, I don't really know of any specific ressources. I've been lucky to be around great marketers so that's how I learned, but I'm sure there are great books out there.
Principe de base en négo, l'un des premiers points du bouquin de Dawson.