Whenever the economy tanks, I get really interested in cash flow. It's a habit that I try to hang onto when things are going well, too, because you can run out of money any time. But there is something about impending doom that gets your attention. Most of the guidance you can find on cash flow is geared to 'small businesses', less than 5,000 employees! This isn't very helpful.
In a nutshell cash flow is predicting your cash-basis profit or loss. It is the nature of predictions to be wrong almost all the time. So a cash flow projection isn't reality, but you want to get close enough that there aren't any devastating surprises.
This simple spreadsheet below is my attempt to get a view of the income side of the cash flow projection. The idea is to quickly allocate your fee for a project over time so you can compare it to the other ingredient - an expense projection.