As the main resource you generate with your business, is money, you want to make sure everything is in order when it comes to having an overview and managing your money. There are a couple of real life best practices I for one have in use for my own personal finances and have seen being used in other businesses as well.
First things first – create at least two separate accounts. One should remain the account you pay your invoices from and the other one is to be used by your customers (basically the account your cash inflows go to). At the end of the month (or week, which ever suits the best) you just transfer all those inflows to your other account you make payments from. This way you have a clear overview and simple structure as to from which account the payments have been done and where the money comes to.
Another thing, and especially important if you’re dealing with physical cash, is to have a clear overview of all your cash movements. The best ways to do it is simple print out bank statements daily or weekly and match all the transactions done to your records. I know there are accounts who reconcile the bank statement to the balance sheet once a month, but I strongly encourage you to do it daily or weekly, depending on the cash movement density obviously.
So, as I said, make sure you manage your resources the best way possible.