What I'm looking for in my betareaders:
* Brevity. One word or point form.
* Confidence. Trust your understanding of the characters and existing worlds.
* Focus. Stick to the precise bit of information necessary, not whatever else may be related/relevant/cool.
* Instruction. We'll figure out the best way to work together, together. Before that, I am watching to see who pays attention.
* Attitude. Please have fun. I truly appreciate your doing this and the work involved. Keep in mind this isn't a job or test, but a chance to be a special part of the next chapter in a story we all love. Whee!!
* Honesty. If you aren't sure, say so. Once the manuscript is ready, be honest about your time and ability to read and respond. If you have any doubts, let me know as soon as possible.