I don't really have any advice, just anecdote.
I suspect that in high school, most of the people I knew thought I was an arrogant know-it-all (because OMG was I ever), and that many of the people I interact with solely online think I'm an arrogant know-it-all (because I have a much sharper tongue online than in person) - but most of my clients don't, and the people I know really well online mostly don't.
If I try and figure out what the differences between those groups are, I come up with these things that are true of the group that doesn't think I'm a jerk:
- I respect them as people, regardless of whether I agree with their decisions.
- I'm not emotionally involved with their decisions.
- I feel that they're trying to do the right thing as they see it, regardless of whether I see that as the right thing, and regardless of their degree of success.
I don't think that actually being smarter is the problem, because I know plenty of much-smarter-than-me people who are the most down-to-earth approachable people you ever met, and plenty of averagely-smart people who are obnoxiously arrogant. For me, the issue to be worked out would not be "I'm smarter than you," but rather "I think I'm right, and you (either outright or by implication) are wrong." And that's not really something to work out with the other person (regardless of the degree to which they're wrong, or you end up like this guy:
http://xkcd.com/386/), but something you work out with yourself.
It took me until I was 33 or 34 and 9 months of CBT (consisting mostly of the therapist telling me to stop talking about what someone else was doing wrong, and figure out what I was doing wrong) to be able to identify any of that, because for a smart person, I'm pretty stupid.
