There are several aspects that are pretty ephemeral...it's just a demeanor and a way of interacting joyfully with people. But, the stuff that I can put into words (and if these fall into place, you'll probably acquire the ephemeral bits with practice):

I love what I sell. And I won't try to sell something I don't love, no matter what it is. If I don't love it, I'm not in the right business, and I'll quit. My current product is one I've been working with for over a dozen years, I've written a (published) book about it, and answered thousands of questions on mailing lists and forums. My appreciation of the product I currently sell runs very deep.

I hate wasting people's time. I hate wasting my time more than anything. So, I qualify people immediately. With my current product, I'll ask, "Do you do any system administration?" and follow up with, "What kind of things do you do?" If the answers don't match what my products do exactly (UNIX/Linux not Windows, website-oriented stuff not desktop or enterprise, etc.), I send them on their way. I'll recommend something else or shrug my shoulders and wish them luck. I won't try to figure out some way to sell them something they don't need. There are millions of people out there who will be well-served by my products...I don't need everyone I meet to buy to make me rich.

I get satisfaction from the whole process, not just the money. I enjoy helping people scratch exactly the right itch. This applies to anything you'd want to sell. At the end of last year, I decided to move into a motorhome and travel the country for a year or two...this meant downsizing dramatically, so I sold thousands of dollars worth of stuff I'd collected over a couple of decades of collecting. Guitars, synths, bikes, antiques, books, furniture, etc. I spent way more time than the money justified to make sure my ads were incredibly descriptive, the photos clear and numerous, and that the person buying knew exactly what they were getting. Some items were only selling for $50...and I probably spent an hour or more on every item I sold, once everything is tallied up. My hourly rate for contract work five years ago was $125/hour, and I wouldn't work for anywhere near that little today...but the process of selling is fun. Coming back to only selling stuff I love and believe in, I took everything I didn't consider awesome to Goodwill or threw it away. I won't sell something that isn't worth talking to someone enthusiastically about. I also like to know a lot about the stuff I sell. A friend asked me to sell some luxury goods she wanted to get rid of at the same time (they were in my closet when I was doing the purge), but I just couldn't do it...I don't know luxury goods and I don't care anything about them. I could never be a luxury goods salesman, no matter how much money was involved.

Of course, the big thing is just practice. I was raised in a world where all the stuff surrounding me, no matter how nice, had a price and was for sale (my mom rotates stuff through her house, so things come and go). I've spent a few hundred weekends at flea markets and garage sales...you can't help but get a feel for negotiation and sales in that environment.