As someone who's been a few different kinds of beta reader, what kind are you looking for?
Do you want someone to read it over for spelling/grammatical/punctuation errors?
Do you want someone to look for plot holes, character contradictions, inconsistencies, or fact-checking? ("They drove the van to the lake, but when they left two chapters later, they were in a car.")
Do you want someone to read it and give you an opinion on the quality of the story?
It's generally not a good idea to expect one person to do all the jobs. Not that your fact-checker can't catch spelling errors, but you want someone whose eyes are focused on a specific task. And while you want someone with good written skills to critique your grammar and spelling, you don't need that in someone who's just giving you an overall opinion on your story. But you would want someone who's done a lot of reading in your genre.
If you want the third kind of beta reader, you can help make their job easier by providing them with a list of questions. Be SPECIFIC. Of course you want an overall opinion, but when you're doing your own final edit, make notes of what page number you're on and what you're wondering. That will help you make your list of questions. It can come out like:
Pg 40: Was the conversation between Jon and Jane vivid enough, or did the humor distract you?
Pg 66: Did you find the appearance of the knife to be too coincidental?
Additionally, keep a list of overall questions like:
Did you find Jon to be a sufficiently sympathetic character to maintain your interest?
Was the relationship between Jane and her brother creepy or just close?
That way, you avoid unhelpful beta responses like "I enjoyed your story!" which gives you nothing. Ask them to read it through and write a paragraph of their overall opinion, then ask them to re-read if they need to in order to tackle the specific questions.
Hope this helps you pick your people. Good luck finding the ones you need.
