If you do nothing else in business, the one thing I recommend to all my clients is to do a simple cash flow forecast.
You can do this by writing down all your receipts and deducting all your costs to arrive at a net inflow or outflow for a month ( or week). You can add the bank balance brought forward to the net inflow to arrive at the expected bank balance carried forward. The balance carried forward for one month becomes the opening balance for the next month.
To see how to do a forecast on Youtube check out the video I did.