how might a human services worker need to adapt their communication approach from one individual to the next?

The key to this question is the word "individual".
Any time you are working with people, to be effective you MUST consider each individual as a special person. What do they need, what do they relate to, what is their background, what are their fears, prides, etc. This is true whether you are in social work, a teacher or selling hotdogs.

To discover what GuruBlue has mentioned, social workers have to ask many questions about why each person is seeking help and what his/her goals are.

I hope this helps a little more. Thanks for asking.