Okay I will give it a try. I just thought about it and wrote down what occurred to me, I assume that there is plenty of room to comment on what
I said or to add more.

Note: There will always be judgment involved, there is always a risk that one inadvertently asks "too much".

What strikes me as less risky:

I liked what Artley Wilkins said. Part of what is okay to ask for is what is within someone's nonprofessional skill set.

Asking someone infrequently.

Asking in a real pinch (as opposed to a crisis) where practical help is really needed.

Asking someone where previous help has been more or less equal in both directions.

Asking someone who has not turned you down recently.

Asking someone who (as far as you know) isn't overwhelmed/very busy with their own issues.

Asking someone who has given you good reason to think that they don't mind being asked, or even like being asked.