Before I enter the house when I come home, I take a deep breath and prepare myself to accept whatever is on the other side of the door, to meet whoever is in the house however they are at that moment. Since I'm often walking into a situation with four kids and lots of chaos, just taking that little mental step allows me to walk in and be available, rather than to walk in with an agenda and try to start controlling things. It's a tiny thing, but it makes a difference in my attitude, and while it may not brighten anybody else's life much, it does allow me to be present for just a moment.
One other thing I do sometimes, on the bus in the morning. I just look at people and wish good things for them for the day. Another tiny, tiny thing which may make no quantitative difference in their lives or mine, but which makes a huge qualitative difference in my availability for conversation (and that has led to some very nice bus acquaintance-ships).