- Is there any chance that the people or businesses you once proofread for might have need of your services on a freelance basis? It's hard to get new clients who value your time and proper compensation in really ANY writing-related field. Best to work with the people and connections you've got.
- Can you very clearly define your niche and any specialties you have that set you apart from ye standard fresh college grad also trying to make a few bucks on fiverr? A background in physics so you know all the long scientific words? Education, so you're familiar with terms and school-specific phrasing? That sort of thing.
It's not quite the same as proofreading, but I do some freelance copyediting in a popular but niche genre of fiction. The way I got the gig was through sheer nepotism - through a friend of a friend, but also we went to school together and copy-edited journal articles together, so it's not as if I was unqualified or given the job sight unseen. And it's for a niche genre that I'm very familiar with, so I know what the audience is looking for and what doesn't fly.
That said, while I enjoy the work as a break from my 'dayjob', it still doesn't pay all that well. I barely make minimum wage for my city, especially after freelance taxes are deducted.