Probably to find your first user. Get feedback from them on your prototype. Startups aren't fungible so more info on your startup would help. Additionally there is a wealth of resources on the Internet: some of my favorites:

How to Start a Startup: startupclass.samaltman.com Watch the whole series, or you might regret it

Lean Startup: http://theleanstartup.com/ Get this book. If you're not a reader become one. Don't skim it; read it.

Founder's Dillemma: http://www.amazon.com/Founders-Dilemmas-Anticipating-Foundat... Read the whole book before you go get married to a cofounder

I have the Lean Startup and I must admit I'm guilty of skimming lol. Thanks for the info/advice. I really appreciate it.

I knew it. Happy to help.

I personally feel that following your own intuition in the first days can be more helpful.

The best way is to share your idea or prototype. In what it consists in?

The whole thing depends on what your product is, what problems are you solving and what touch points have you identified for reaching out to your target market.

Who did you build it for? Who is the customer? If you don't know find a rough definition. Then you know who to sell to and that is the important step :)

the basic idea of startups is making more than enough money and you do that by seeking funding first. But once you do that you have to answer to somebody... to shareholders. Also as things can grow, you'll have to manage employees.

ask yourself if that is what you really want. YCombinator is close.