The title of this post may seem counter-intuitive, but the biggest mistake most "sales people" make is to pitch the client on all of the bells and whistles of their product without ever finding out exactly what they were looking for in the first place. A perfect example of this is the pool cleaner pitching his services to a home owner. The pool cleaner went through his entire presentation fully explaining why using him to clean the homeowner's pool would be beneficial to him. By the end of the presentation the homeowner was impressed and told him, "That was an exceptional presentation, and if I had a pool I would definitely choose you to clean it."
Sometimes we are so sold on our own products that the excitement can make us forget all about the client. We have to slow down, find out why the client needs our product, and then use the information we have to mold our benefits around the clients needs. There is a quote that says "Sales is finding a need and filling it". This is only partially correct. It should say "Sales is finding a perceived need and filling it". If the client isn't even aware of the need, then there's no way we are going to enlighten him in a sales presentation. Instead, find out what the clients perceived/actual needs are and when you find that out, show him how your product accomplishes those needs. Not only will you build value in your product, but you will also let him know that you are listening and that you care.
The easiest way to find these needs is to just ask questions and LISTEN. If you ask the right questions, people will tell you everything you need to know. The first and easiest question is to just ask them why they think they need your product. They will proceed to tell you exactly what need they are trying to fill and as long as your product does that, you should be in good shape. But don't stop there. If your product not only handles that need, but also accomplishes many other useful tasks as well, then the value will only continue to increase until the customer cant help but buy.
So remember, sales is not about how good you are at speaking, but how good you are at listening and asking the right questions.