The idea of doing no harm seems so simple, but it applies to people who "just want to help" very clearly: sometimes, we want to help so bad, to make the hurting stop, that we go a bit overboard.
There are things we can do that will never do harm to a person who comes to us: listening is the top thing that we can offer that does not harm. Just being there for a person, lending an ear and refraining from judgement can account for a great amount of healing without damaging the person more than they may already be damaged when they come to you.
Many times, though, the harm that can be caused in a clergy-lay relationship isn't about someone who is already in pain, but about accidentally cauing pain through the relationship. The only way to truly avoid this is to treat every person exactly the same, regardless of who they are: make time for every person in your Grove (or in ADF) in the same way you would for any other person in the same group. Don't hold grudges for any reason.
The most important thing, though, is simply to understand that as clergy we need to be close to our members, but also impartial and distant. We can't play favourites, and we need to provide the same services to anyone in our congregation that we provide to anyone else.