Easily done and can get started right away. I do a lot of proofreading on a weekly basis for a company I have been working for a year now - it's mostly advertising sites.
I have a degree in languages at the University of Ljubljana - Department of Philosophy, for which I can provide proof if needed. I do a lot of translation work and am completely focused on English to Slovenian and vice versa, which involves having an excellent grammatical basis in both languages.
I am a native speaker from Slovenia and have completed countless translation projects, my recent one being translating a mobile app for Cybo. I have also translated (which of course includes proofreading) the whole onlinecasinoadvice dot com page and their financial and legal documents, and have been hired by freelancer dot com to localize this page. Right now there are two of us working on this project, which means we have to constantly proofread each-other's translations and correct them.
I have been an employee of translatecompany dot com for five years+ and have translated an abundance of documents, both financial and legal for various physical and online companies, all to the satisfaction of my employer. And since I am not the only employee at the company, I also get plenty of text to proofread which others have translated.
Honestly, compared to translating, proofreading is easy ;)
I am also a published author, so I know my way around the English language quite well.
I hope we can work together soon!