Total headcount per client. If you're a one-man-army entrepreneur who plans to grow the business on your own, pay special attention to this ratio. Divide the number of employees at your company--just one if you're a jack-of-all-trades--by the total number of clients you have. Ask yourself if you'll want to be managing that many accounts in five years when the business has grown. If not, you'll need to revisit your assumptions about revenue or payroll expenses or both.
Building an accurate set of growth projections for your startup will take time. When I first started my company, I avoided building a detailed set of projections because I knew the business model would evolve and change. But I regret not spending more time on business planning since I would have avoided several expenses along the way. The company's board of directors now requires me to prepare quarterly updates to our financial projections. Now when I lapse into fits of audacious optimism, the projections force me to forecast what these dreams mean for the company's bottom line.