Usually when I want to offer advice I start with "Name, may I ask you something?" More often than not they are okay with me doing a follow-up and having a conversation on it, or just say nothing, where I won't bother. I think the only time I don't ask is with a tank with a badly underleveled weapon (Read, 15-20 levels below. Not ilevel, actual level) since it affects their abilities to do things so much. I can't recall ever having someone complain at me, and have actually made a few friends just trying to help.