Spelling and grammar - you'll just be fixing the spelling and grammar in the fic

Characterisation - are the characters in-character, do their motivations make sense etc

Plot - Are there any plot holes? Does something not make sense?

Continuity - Is there anything that's inconsistent in the fic? Are the characters in a restaurant and then suddenly on the street with no explanation, did character A pick something up twice in a scene etc

Style - This should be agreed upon between author and beta as to whether it's wanted. The beta suggests style changes e.g there are too many adverbs used in a sentence, suggestions of changes to dialogue, structure etc.