There are many good answers listed here already. Like some have said I don't know that there is anything that will "insure" success. But I can tell you if you want to succeed the key is "follow-up". 

It truly amazes me how many fail simply because they did not follow up. Most people follow up once, twice maybe. Rarely three times yet statistically it is proven it can take repeated follow-ups before someone responds.

This doesn't only apply to sales either. Vendors, Customers, Employees, Investors, you name it. If you will just follow-up in whatever it is you are doing your chances of succeeding will increase many times over.

A second to follow-up is, "take action". So many times we plan, and plan, and plan but we never take the action of implementation. No plan is ever perfect so Just Do It.

Anyway, that's my take. Hope it helps.