As a reader, I'm thorough, patient and extremely vigilant. I will be honest about areas of improvement in someone's work, but strive to be as respectful as possible. Whether it's a review of grammar / style basics- or something more in depth, such as assistance with story framing, character development and writing style- I'm more than willing to lend a hand. That being said, I do have some expectations:
1) I will not beta-read stories that are not subjected to basic spell-checking. Occasional typographical errors and misused homonyms do happen, but if the story contains ubiquitous spelling errors, I won't work with it.
2) If I beta-read a story, I expect that the author will be able to discuss any critiques maturely. I'm here to help improve your work, not parrot meaningless compliments. If any part of my review/comments is unclear, please do reach out to me for any guidance.
3) Depending on length, I anticipate a turn-around of no less than a week to critique a chapter. If I think it will take longer, I'll be up front to let the author know.
4) If I'm not familiar with the original body of fiction, I will at least familiarize myself with the basics before beginning the beta-read. I will expect the author of the story to have done the same before writing the story. For example, I will expect any non-original characters and places to be spelled accurately.
5) I do not do collaboration work. If you have a story you'd like me to beta, I am happy to help, but I am not interested in becoming a main contributor of original story content and development. Firstly, it is supposed to be your story, not mine. And secondly, I typically have several projects of my own in flight at any given time, and my primary focus is on developing original content for those.
With all that out of the way...one last thing: If you contact me to be your beta, I will be asking you some serious questions about your level of commitment to your story before I will agree to work with you. Do both of us a favor and be honest and realistic with your answers. Now, I'm not expecting that writing fanfiction is the single most important priority in your life (really, I hope it isn't), but what I'm aiming to find out is whether you really intend to see it through. Is writing your passion and you're hoping to improve your skills...or is it a casual hobby? In the case of the latter...I'm not the beta for you. It's not fair to ask me to invest a significant chunk of time to orient myself with your work and what you plan to do with it up front, and then have you lose interest in the project a few weeks later.