You are just starting out and want to test the waters.
You have some writing experience, but no proofreading training.
1. Workplace Grammar & Style
2. Proofreading Power
You might have a college degree.
You consider yourself a decent writer.
You might have some freelance or everyday proofreading experience, but not for paying clients.
2. Business Grammar Essentials
3. Proofreading Power
You might have a college degree in English or journalism.
You might have worked in a writing or editing related job.
You want to seriously pursue proofreading or copyediting jobs or start a freelance career, but you need more credentials.
3. Professional Writing Style
4. Proofreading Power