Cash is king, particularly in the current climate. Do you know how much you are likely to collect from clients, and over what period?
If you do not already do so as a matter of course, go through your aged debtors list, and find out how much is realistically payable. Chase sooner rather than later, initially as a polite reminder, but later in a more businesslike way. If you have business clients, they will not respect advice from someone who does not manage the lifeblood of their own business.
Write off what you have to. It is painful, but at least you will be left with real figures.