Focus on cash flow. I understand the difference between cash flow and profitability, and I'm not recommending that you strive for a lack of profitability. But cash is what keeps the doors open and pays the bills. Paper profits on an accrual accounting basis is of no more than secondary or tertiary importance for a startup. As my mother used to say, "Sales fixes everything."
Source: Five most important lessons I've learned as an entrepreneur: http://www.sun.com/solutions/smb/guest.jsp?blog=five_lessons
Contributed by: ~C4Chaos