So I’m in the freelancing and online business game for more than a decade. Same as everyone else, I started as a rookie, making the same rookie mistakes, which were then reflected in my monthly earnings (or absence of them). A typical mistake is starting the work without receiving payment from the client. I'll show you how doing this will cost you thousands of dollars in the long run. And yes, I have the exact numbers.
Personally, for projects under $1,000, I require 100% of the payment upfront. For bigger projects, I define milestones with the client and the payments arrive in chunks, but are still paid in advance. But most of the time I work through the Codeable (WordPress outsourcing platform), where you need to pre-pay the full amount into escrow.