Also how do you work with 'online contracts'? Or do you just trust people? Is this best way to email details of what work you will carry out to the client and them agreeing to it in theory are signing the contract.
People differ on whether it's 50% or some other percentage, but for fixed-price bids, I always do 50% before as deposit, and 50% after completion. For on-going work, minimize your exposure to non-payment so you can do weekly or biweekly invoicing and billing. That way, in event of non-payment, you've minimized potential losses.
For online-only work (where you haven't met the client face-to-face), you still should get a contract, and still do the same with deposits and all that.
Trust, but verify. Don't put yourself in a position to get screwed.
I've seen people use Freshbooks which allow invoicing and payments together, so you keep all that admin under one system.