Having run my own consulting company and been part of several start ups at this point in my life, I can't emphasize enough the need to focus on accounts receivable.  This is the life blood of your venture and your ticket to freedom (if you are venture backed) – inbound cash flow.

Yes, it is important to get that first customer or client but pay attention to payment terms and cash flow implications.  Big companies are big and don't always promptly pay an invoice…so be diligent and understand that your near term cash needs are not the most important thing for your customers.

Be creative, structure pre-pay agreements, and provide incentives for early or complete payment.  It will benefit you in the long run.