Whatever the case, make sure to invoice your clients consistently. You're more likely to get paid on time when your client receives invoices regularly on the first day of each month, than getting them sporadically.
Terms (or Payment Terms): Invoice terms depend on common practices of your industry, your relationship with the customer, and your cash flow needs. For example, “Net 30” means that the invoice is due 30 days after the Invoice Date. Be mindful some businesses may pay later than the stated due date, so you may want to include a buffer to keep your business free from a cash flow gap.