Alan Ennis, who ran the make-up company Revlon from May 2009 until he resigned in October 2013, says it doesn't matter what your company does--you could sell lipstick or screw drivers. Regardless, there are several rules every CEO must follow to be an effective leader.

In a recent interview at the University of Pennsylvania's Wharton Business School, he spoke about his tenure as CEO. At the root of great leadership, he says, is the ability to stay calm, be honest, and work with your employees to stay ahead of market trends. To do that, you ought to follow these four rules:

Be comfortable being wrong.

Ennis says that his leadership style is unique--he doesn't rule heavy-handedly and makes decisions with his employees. "It is founded on a very basic principle, which is that I'm not uncomfortable being wrong. I have a leadership team where I tell them regularly, 'Listen, guys, I'm going to be wrong half the time. And if you can be right half the time I'm wrong, then we'll be right 75 percent of the time.' And making three out of four decisions correct in the corporate world today is a pretty good thing," he says. "So, I think I inspire my leadership team to be opinionated, to be vocal, and to challenge me. This also benefits them because they feel like they're playing a role. So, there's a CEO and then there's the CEO leadership team that leads Revlon. That's sort of unique. I avoid people leaning where they think I'm leaning, and we therefore get better results."

Know your finances.

Ennis came to Revlon as the CFO in 2006 and became the treasurer until 2009 before taking up the CEO reins. He says that his finance background was a strength that all leaders could find helpful. "It's all about making money--money in the form of shareholder wealth, in the form of free cash flow to reinvest in the business or to buy additional assets," he says. "It doesn't matter whether you're selling a lipstick or a screwdriver; it is about how you sell more of them at a higher profit margin per unit. I think a big part of any business is the financial underpinning. Finance is a very good basis and a very good foundation for any general manager of any business."

Know your product, even if you have to wear make-up.

Ennis admitted that it was difficult being the CEO of a make-up company as a man--he couldn't identify with his target consumer's needs. But that didn't stop him from getting his hands deep into the products. "In reality what I do is submerge myself in the category," he says. "I can be spotted daily working on wearing different types of nail enamel that are supposed to exhibit different characteristics. In our product commercialization process, I actually try all the products. I've become very adept at putting on mascara and eyeliner. I take it off most of the time before I go home on the train."

Bake innovation into your strategy.

A great leader makes sure continued and consistent innovation is part of the business strategy, Ennis says. "It’s about bringing news to the consumer, whether it’s in laundry detergent or Pampers or toothpaste--whatever it may be," he says. "How do you bring something to her that solves a problem that she has? How do you bring mascara that is both volumizing and comes off easily but doesn’t stain in the rain? How do you bring a lipstick to her that’s long-wear but doesn’t feel tacky at the same time?"

Revlon bakes innovation into its strategy by maintaining a three-year rolling portfolio plan for all its brands. That serves to reinforce the idea that the goal is always to think about new technology, new formulas, new packaging--anything that will reinvent a category or give a new spin to an existing category.