Generally, a proofreading job comes with specific requirements from a client. When I start a proofreading job, I always keep these ones in mind, as well as making sure I do not make any preferential changes unless these improve the overall quality of the text and benefits the end user.

Proofreading involves more than correcting orthography, or grammar mistakes. It involves reading the text as an end user, and making sure the original message has been accurately conveyed into the target language, while also localizing and adapting the tone to the target culture.