For recurring jobs take 1 month of pay in advance or bill weekly or every other week, whatever you can afford to loose.
For small projects double your price before communicating it to the client and take 50% as advance. Most likely client will pay but you'll have two times as much work as you initially estimated. Sometimes client won't pay, but then you don't need to go extra mile to make him happy so you won't work as much and price will be fair anyways. If your client turns out to be awesome offer discounts at the end of the project. Customer will love you for that as much as you came to love him.
For small projects double your price before communicating it to the client and take 50% as advance. Most likely client will pay but you'll have two times as much work as you initially estimated. Sometimes client won't pay, but then you don't need to go extra mile to make him happy so you won't work as much and price will be fair anyways. If your client turns out to be awesome offer discounts at the end of the project. Customer will love you for that as much as you came to love him.