As soon as you become a freelance writer and get an order, you should let your client know the way you would like to receive payments. Specify it, whether it will be Paypal, bank transfer/wire transfer, cheque or any other way convenient for you. This will allow clients to make appropriate arrangements on time. Moreover, this allows you and a client to discuss and come up with something that is convenient for both of you.
If you work for some freelance community, you usually receive your payments not from a client directly but from the company because they find clients for you. And they guarantee that you will receive your payments twice a month. In most cases the orders that are processed from the 1st to the 15th of the month are paid on the 1st to the 3rd of the next month, and the orders processed on the 16th and the 31st of the month will be paid on the 15th to the 18th of the next month. But different companies offer certain methods of payment, for example only Paypal or wire transfer. You should discuss it with the company before performing the first task.
We wish you success in your freelance writing!