I don't want this to sound harder than it is, because it's not super simple, but it's not super complex either. But when it comes to keeping an eye on cashflow, my best tip is to actually do a budget.
From a business perspective, if you're using accounting software like Xero, it's relatively straightforward to go into their budget section and work out what's your projected income (or sales or revenue) and then what are all your expenses - and you can do it month by month. When you do that budget, It's just really simple to see what your profit is going to look like, or what your net profit is going to be after all your expenses. Once you know that and it's relatively reliable, that's what you work towards. In fact, once you've got your budget sorted, we can work out what your weekly magic number is.