Honestly it's better to keep things to yourself unless the issue is making the content impossible to do. I see people play badly all the time but it's just not worth the hassle of dealing with the drama of unwelcome and/or unrequested advice when you can just ignore it and finish the content without much trouble.

I have found people are rarely receptive to advice unless it's painfully clear that a huge problem is taking place. When an obstacle cannot be passed, people are more likely to consider other options because they have no other choice unless they want to leave.

And some people can't take any criticism no matter how it is presented to them.