It’s a tricky question given there are so many variables and I don’t know what industry you are in. Some thoughts:
1. Focus on marketing to existing customers – Direct digital mail, messaging etc.
2. Review pricing and bundling of products/services – how can you offer more value now and solve new problems customers have
3. Test low cost, highly targeted campaigns in digital – Facebook, Social… etc.
4. Take advantage of lower costs in traditional media to promote
5. Start calling most recent customers to check-in and see if they have needs you can satisfy
6. Engage in “softer” communications – tips, advise, thoughts. Engage existing customers in conversations.

Before doing any of that I would:
1. Lower all fixed expenses immediately – cash is king!
2. Defer all fixed expenses where you can (rent, payments, etc.)
3. Lock on what you will have to sell if suppliers aren’t supplying