To increase sales & more customer acquisition
It really depends on your target (B2B, B2C, B2E) and where you are in the company cycle. There are 4 distinct sales processes - Founder, Explorer, SWAT, and Infantry (cribbing from Geoffrey Moore) and each model has a different process. A simple, but normal mistake is for a startup to hire a "sales force" (the "infantry") before understanding how to sell the product and to whom.
In my experience (started selling door to door at 6) you never need to "motivate" a great sales person - we do/did it for the thrill. What you do have to think about is how to compensate them, an entirely different issue.
However, be very clear; you cannot motivate people to sell things that the market you think you are after does not want to buy.
Always incentivize the behavior you want to occur. There are a lot of sales compensation strategies, however each one motivates a different pattern of behavior. There's a difference between generating leads, making calls, closing deals that are small, closing deals that are big, providing excellent customer experiences, and getting customers to pre-pay. You might want your salespeople to do all of these things, but you will only be able to incentivize one or two of them at a time. Decide what's important and what you need versus what's nice to have. Don't be afraid to talk to your salespeople and find out what they're struggling with so you can understand how to support them.
You need to enable your salespeople, push them to excel, but don't set them up to fail. You are responsible for refining and perfecting the sales process, for listening to sales calls, for providing supportive marketing materials, for driving interest in your product. If your salespeople are outbound or inbound it will make a difference in what they expect. Get to know each of your salespeople individually. I can guarantee they are personally motivated by different things. Money is not the only thing that motivates a salesperson.
Make sure your distribution of risk is fair. An order-taker is not a salesperson, but you shouldn't expect your salesperson to do all the work to find and win customers either.
The other posters have said it perfectly. If I may add a couple more which someone already touched on:
The Product - this must be brilliant. It must be better than the rest. Remove your rose tinted glasses and view it against your competition. I quite recently worked for a company where I was selling an investment product to financial advisers for their clients. Naturally the advisers wanted to see what was the typical performance of my company's investment product. I could not and would not skirt around the issue or I would lose my reputation. I could only show them the truth upon which the nice advisers said they'd think about the not so nice openly laughed out loud. I could talk about "de-risking" the portfolio and that's why the performance wasn't so good and all sorts of things, but at the end of the day the product was not good enough.
And that makes a sales persons job very difficult.
They become despondent, they say "what's the point?" you can throw all of the bonuses at the world at me "if I perform" but it's futile if the product isn't sellable. So.. make your product the best.
The other point is to show them appreciation when they do make a sale. I don't mean taking them on 5 star luxury breaks, just a "very well done on that, my hat goes off to you, and I know how hard you worked on that, so well done again."