Beta readers (or critique partners) are invaluable, and not only for their “editing skills” but also for something that I’m fortunate to have gained with my betas . . . friendship. We email, text, and talk on the phone. Sometimes, it's about writing. Other times, it's about family and life outside the writing world.
But as for the "beta-ing" part of beta readers....here’s my list I’ve what I try to help with when I beta
and what my betas help with when reading my manuscripts: 
spelling
grammarplot
dialogue
characters
flow
voice
word choice
word usage
continuity
ideas
The beauty of having more than one beta to read your work is that what one may not see, another may catch, and vice-versa. In essence, betas are a set of fresh eyes and ideas.
Also, beta reading is a perfect opportunity to give encouragement, advice, support, and to cheer each other on when we may feel like throwing our WIP in the pond. :D
I have three wonderful betas.
Two have been with me through this craziness for a couple years,
and one I recently started swapping material with.
I wouldn't trade these amazing people for the world.
I heart my beta readers and am honored to call them friends. :D
