You have to think and act like an entrepreneur.

Starting a company is tough.  It takes lots of hard thinking, lots of busy-work, and lots of time.  It's not a 9-to-5 job, and it will be taxing on your marriage and family life, if you have one.  You will be thinking about the job almost 24/7.  And you will absolutely love it, which enables and justifies this commitment.  Now, if this description doesn't fit you, then you probably aren't a 100% entrepreneur.  Sure, you can put your toe in the water and be half-committed, and maybe you'll be successful (or ride on the coattails of others who are committed), but most companies these days don't succeed with a part-time effort, and if you're the only one who isn't committed, then your job is in jeopardy.  No easy ride.  Feel free to reply with any stories or insights you have on this topic.

But I don't know how to do that.

Starting a company requires many disciplines, not only in the formation and administration of a real company, but also in solving some of the really hard issues that your company will encounter.  Whether it's how to enter a certain expense into your finances, or even finding a bookkeeper who knows how to do this, or solving a technical hurdle that your technologist just encountered, or whether you're suppose to draft a term sheet first (or let your investors do it), don't think that you have to know all of the answers.  Your first go-to place should be your co-founders and your own database of contacts, then your board, if you have one yet.  These sources will probably have a vast database of contacts, several of which will have your answer, perhaps after one more level of reference to the right person.  Don't hesitate, thinking that they might think you should already know the answer.  Few CEOs and founders can run a company without support.  Tap these resources for your answer and move on to the next challenge.  Now!

Analysis Paralysis!

Okay, I can be nerdy and analytical, too, wanting to test, optimize, test, refine, test... all to make the product even better before I finally release it to customers.  But it's easy for this process to continue with no end in sight.  At what point do you say enough?!  "But the customer would love to have this new bell/whistle that I just thought of."  "But I need to try this slightly different formulation...I think it will work better."  Enough already.  Save something for a follow-on product.  Get the product out-the-door, and get some feedback from your customers before you do any more analysis/optimization.  That feedback is so much more valuable than continued optimization in a vacuum.