Many new sales people tell me the toughest thing about sales is the rejection, or "no" they receive from a prospective customer. When I hear "no" I consider that to be an opportunity to provide a better (or different) value proposition or ask the prospect who I can talk to that would be interested in what I have to offer. While they may not be interested in what you're selling, someone within their organization, industry, network or neighborhood might....you'll never know until you ask.
The bottom line is never give up. Be respectful and put yourself in your prospective customer's position. Sometimes a customer just doesn't have a need for what you're selling....knowing that you can't win them all will help you stay positive and move on to the next prospect/opportunity.
One of the most valuable tools I use is the referral. That referral might be from an existing customer that likes and uses my service, it might be referencing an article I read about a company similar to theirs that could benefit from my services....letting a new prospect know that there is someone else out there who either has or may use your services for the benefits you offer can help you get your foot in the door. Of course once your foot is there, you need to offer something that can help the customer be more....efficient, save costs, solve a problem, boost revenue.....whatever it is you're offering has to provide value.
Find the customer's problem and help them solve it! Turn the "no" into a referral, and always stay positive!