Start with a few real classics:
1) Zig Ziglar - Secrets of Closing the Sale
2) Tom Hopkins - Mastering the Art of Sales
Some more modern books:
3) Seth Godin - Small Is the New Big: And 193 Other Riffs, Rants
4) Rich Dad's Advisors: Sales Dogs
5) You, Inc.: The Art of Selling Yourself
Any entrepreneur needs to learn sales, because you will need to sell your vision to your employees, yourself to your investors and your product to your customers. While the first two are all about self confidence, the third is the one you asked about.
Selling is like swimming... You can read a lot of books about it, learn about hydrodynamics and what not, but until you jump in the water, you are not going know how to swim. To keep the analogy going, you might not want to jump off a boat in the middle of the ocean and start swimming to shore as you start... Start with a teacher and a lifeguard near by... Start by selling other peoples products before trying to sell your own. One class of product that I generally resent but can give you great experience is MLM (Multi-Level Marketing). You can learn to sell that junk to strangers with little personal financial risk, and they will teach you courses on sales for almost free (just your time and maybe a small initial investment).
You can either gain the experience you need, or partner up / hire someone with that experiences. If you have the tech background that is needed for the business, you might want to focus your attention at that, and find someone else to take care of the sales/marketing/business end of things, since a good CTO is also critical. Keep focused on your core competencies, and you will do well.
Great salespeople aren't born, they are created. None Of us likes rejection, and that is what defeats most folks from being successful in sales.
There are a number of widely available sales training programs. Sandler Sales Training, a franchise, has incorporated most of the basics and is available almost everywhere, but there are others.
Just keep in mind that the stereotype of the sleaze bag who foists off unwanted crap at inflated prices (Glengarry Glenross) is mostly a media creation. Top notch, successful sales people believe that what they are offering solves the customers needs, and does it better than alternatives. That's why entrepreneurs are frequently successful selling their wares, even though they aren't polished in technique. You gotta believe.
There are three steps to every sale:
1. Why buy anything?
2. Why buy my product?
3. Why buy now?
The first is about convincing a customer they have a problem and that your solution will solve their pain. If you can't do this then go back to your previous job.
The second thing you need to do is convince them that you're better than the competition. Very few people buy without considering their alternatives. Thing about how you buy in your personal life. You ought to be able to win 33-50% of these in a nascent market.
The third item is the death of most startups. They don't know how to convince customers they need to buy NOW. I call it creating a burning platform.
I cover the whole topic in my post teaching sales lessons for early-stage tech companies.
Just a quick response to something RonGa’s post.
RonGa said, “You can learn to sell that junk to strangers with little personal financial risk, and they will teach you courses on sales for almost free (just your time and maybe a small initial investment).” I understand what you are saying, but IMO these are the kinds of things that give professional salespeople a bad rap. You should never “sell” anything to anyone that they do not need. It’s your job to qualify the customer, do the homework, and make sure your product has a benefit to them. You want customer satisfaction over the long term. This also helps you build your personal brand which will help you even if you switch industries. The people you sell “junk” to now may be the CEO of a company you want to do business with in 10 years. Always hold yourself to a higher standard.
Familiarize yourself with the 7 steps of selling (plenty of Google references). Keep in mind, asking for things and persuading others is something we all do our entire lives. So you have more of a foundation in the basic principles than you realize.
How did I learn sales? Throw yourself in the deep end! And remember, you are never 'too good' for anything! (I will explain in a minute)
I started my first business when I was about 15. How did I find clients? I just went door knocking on businesses. Very quickly I figured out what works and what does not.
When I finished high school I took a job selling door to door (to business) on a mostly commission basis. I think EVERY entrepreneur should have to do this. You are not too good or too high and you will learn some incredible lessons here that will help you forever. Every time I launch something new I'm back out there hitting the doors.
Just remember, always be honest. Be straight up. Build a relationship before selling (if it is a large sale don't even mention the product in the first contact). Reading people comes with experience. I'm not a fan of spray and prey for business but it will teach you plenty if you are new. And you will no longer fear rejection (if you think you have been rejected but never gone door to door then you have NOT been rejected). Another valuable lesson that transcends sales!
The first step is to understand what sort of sales you need to learn. This will depend on what you're selling is (enterprise software costing $100,000 or $1.50 iPhone app), who your customers are (oil company CEOs or 16 year old kids), what stage your product is at (buggy, early stage or stable, mature late stage) and so on.
A good place to start understanding these issues is Selling the wheel by Jeff Cox.
read how to win friends and influence people, then get out there and fail. lots. you'll learn far quicker than reading some book on how to sell.
I'd strongly recommend having some experience in sales or marketing before beginning your own startup.
In my case, I worked for a software company as a developer and tech support person for several years. But whenever I had an opportunity to help out the sales team on a proposal effort or participate in a sales presentation as a technical expert, I did.
The insights I got from those experiences have helped a lot in my current startup. I knew roughly how the sales cycle in my industry worked, and got a rough appreciation for which sales approaches worked and which didn't.