In March, when the coronavirus began wreaking havoc on businesses across the U.S., Barbara Corcoran started calling the leaders of her companies--all 78 of them.

While the Shark Tank investor's best-performing businesses were already scrambling to adapt, many of her other companies were taking a wait-and-see approach. The conversations served as an early indication of who among her entrepreneurs would have what it takes to respond with confidence and who wouldn't.

"It really separated the men from the boys and the women from the girls," Corcoran says. "Some people just have the ability to turn on a dime and be ridiculously optimistic, which I'm beginning to think is half of everybody's success." In the past six months, Corcoran has learned many lessons about what works for businesses in a pandemic and what doesn't. Here are five of her tips for how to survive and thrive in the Covid-19 era.

1. Throw away your business plan. 

One of the first things Corcoran did in March was to have her entrepreneurs make a list of all of their sources of revenue, and then throw it out. "Assume nothing from that list is ever going to happen again," Corcoran says. "Where else could you drum up some business?" In many cases, her entrepreneurs came up with new direct-to-consumer opportunities and ways of engaging with existing customers, as acquiring new customers is about four or five times the cost of keeping an existing customer. 

2. Call your landlord.

Many of Corcoran's entrepreneurs have struggled to make rent payments for their businesses since the beginning of the pandemic, and even the ones that haven't expected to run out of money for rent eventually. The minute you think you might have trouble making a rent payment in the future is the time to call your landlord, share as much data as you can about lost income, and respectfully ask for flexibility, according to Corcoran.

"You have to remember that every landlord right now is frightened," she says. "That gives you tremendous leverage as a business. No one wants empty space right now."

3. Learn to sell on camera.

With video conferencing largely replacing in-person communication, many entrepreneurs need to learn how to effectively pitch their product over video. Corcoran credits one of her Shark Tank entrepreneurs, Kim Nelson, the founder of the online handmade cake company Daisy Cakes, with helping Corcoran's other entrepreneurs get comfortable selling on camera.

"She was able to teach people how to display product and how to get people to look, feel, and taste it when you can't really do it in person," Corcoran says. 

4. Come up with a best-case/worst-case scenario.

During the pandemic, Corcoran has advised her entrepreneurs to devise two plans: one that assumes the best possible outcome for the next six months and one that assumes the worst possible outcome. This way, no matter what happens to your business, you won't be caught completely off guard.

"Plan for both, because there is no predicting what's going to happen," Corcoran says. "It depends on the coronavirus vaccine more than anything else."

5. Focus on staying in business.

While it's the job of every entrepreneur to position his or her business for long-term growth, keeping your company afloat in the short term is a better strategy during the pandemic, according to Corcoran. There's simply too much uncertainty to be able to focus on long term results.

"You'll go crazy trying to control something you can't," Corcoran says. "Whatever is going to help within the day or the week is what I get people to focus on, because I believe that does make the biggest difference."