5 Best Practices in Freelance Editing
Ask the three key questions - By When (deadline) | How Much ($$$) | How Many (words)
As a freelancer, you must narrow down these three things right at the beginning. If not accepted and cleared by both parties, it leads to a lot of heartburn and frustration later. Besides, it turns the project proposal into a concrete, objective numbers rather than subjective figures.

Complete pilot projects of at least 1000 words
Pilot projects help you and the client get a feel for each other's working style. They help you, as a freelancer, have a ready reckoner for the big league match. As for the client, he can gauge your technical mastery and abilities at minimum risk, without committing much money.

Research your client
This is Human Resource 101. As a good prospective employee researches the company he's got an interview at, so can you research your client on the internet. Look for the articles they might've written, the places where they've been featured. This will help you communicate with them much better, since you're not starting off on a fresh slate, but have done your homework.

Work in Google Docs
As of writing, I have not found a better tool to collaborate over word documents. This incredible tool by Google has helped me work with clients from the United States of America, United Kingdom and even Italy! The boundaries between countries are no longer an excuse! One thing to keep in mind, though, is if you're editing a book, or something large (over 30 pages) in terms of words, you are better off dividing the book into different documents of two chapters each. The tool really falters at large documents, and even reverses updates done to the document, when downloaded. Causes a lot of frustration.

Communicate via Slack
Its quite likely that you will find your client via LinkedIn. But do the long conversations you will have (hopefully) with your client need to be restricted to LinkedIn's clunky Messaging tab? Absolutely not. It is always best to set up a channel on Slack or one such team-messaging app. Helps keep things light and flowing.
Be like water, my friend. - Bruce Lee

Use The Right Medium For Payments
Five projects into my freelance editing gig, I have found two tools that are the absolute best for transferring payments. If your client's based in India, and paying you in rupees - Instamojo is your best bet. Love the simplicity of their platform, with minimal fees charged.
If you've gone international, and have a client paying you in any currency other than INR, TransferWise is the way to go. Unlike Paypal, which is the biggest player, TransferWise is much more transparent about their fees, and what you will actually get in hand after factoring in conversion expenses.

That's it! You're all set to make your mark in this up-and-coming industry, with all the buzz around content writing. Do comment below with any tools that have helped you as a freelancer.