I try to do a balanced approach and point out both the things that work and the ones that don’t.
I like to give examples of how I might fix something that seems off, not because I want the author to adopt my style, but because I’ve found people learn better that way. You can tell someone to show and not tell, but I think it’s even more helpful if you can give them an example of what you mean. It’s often so hard to see the flaws in our work, and I think examples help to clarify exactly what could use tweaking. Of course, the person I’m critting can take my example and use it verbatim, or throw it in the proverbial trash. 🙂
I don’t seek out grammar etc errors, but if I see them I have a compulsion to point them out. That said, if there are an abundance of them, I’ll probably put a note that says, ‘I’ve stopped critting grammar issues here,’ just so the person knows.
I’ve been told I’m good at pointing out inconsistencies, whether big or small, along with OOC actions.
I’m a huge fan of track changes and comments in Word, which is how I do most of my critiques.
I also like to throw a little humor in my crits. Writing is supposed to be fun, right? 🙂