I have a couple more to add.
1. If you're at a store and need to check out, end your conversation, or at the very least, put them on hold and interact with the cashier. You know, treat them like a human being.
2. If I am on the phone with you, pay attention to the conversation. My SIL is terrible about this. I will call to talk to her, then when her husband walks in the door, she'll ask me to "hang on a minute" then have a side conversation with her DH. The worst part is that I can hear the conversation and it's usually something trivial, like did he see that she bought cookies, or the car needs gas, etc. I finally started hanging up on her if she leaves me hanging for over 2 minutes.
3. I hate call waiting. It really makes me feel like the b-list conversation when you say there's another call coming in and then leave me on hold for 5-10 min.