Develop executable strategy and prioritized action list... The devil is in details of course.
And lots depend on the field and type of business you are trying to build.
I mentor a lot to startups and formal accelerator programs. Glad to discuss if there is an interest.
a) Look for a customer that will not only be a customer, it will be your first and most important ally as a word spreader of your company and give you reputation. It may not be a customer if you are not selling to companies.
b) Pre-sell services/products to fund your early stage operation
c) Develop no-core products/services that will help you fund the company while you are developing the star product
Just a few most rapid growth entrepreneurs usually use.