Just about all businesses allow for a 30-60 days payment of goods. Although this is the standard way of doing business, it can create a cash flow problem when your customers fail to pay you on time. If everyone paid when they received, this would not happen. It comes down to proper management of this system to keep you business working smoothly.
You can try asking your customers for a down payment when the service or product is received. This can help with the waiting time for the rest of your payment. You can also try an incentive of a discount to those who pay they bill in less time.
A statement can be sent to them the day your product is sent to them although some businesses will mail reminder statements a few times a month. Any unpaid balance could generate an interest addition and might generate earlier payment from some customers. Another thought is to not allow any new orders from a customer who has yet to pay for the last order. This will only add to an already late payment and the snowball begins.