Based on my experience and from what others have told me, one of the best jobs if you want to learn how to interact and deal with people is to be a server at a restaurant.
It takes a lot to do the serving job well, you have to learn how to:
1) Communicate well, both listening and speaking
2) Keep track of many different tasks at a single time (put in orders, take out orders from the kitchen, get someone extra sauce, etc)
3) How to make people happy, especially when they're upset
Those are just a few things you'll get better at by being a server. I had five jobs before I started my career in tech, and serving in my opinion was the hardest, and I didn't do it for as long as the other jobs I had. But I'd be lying if I said it didn't teach me the most about human to human interaction.
A side bonus to serving is that you'll have much more respect for the people in that industry. It's not easy, and it's not the best paying, but being able to understand the waiters and waitresses serving you will help you make their lives easier, thus resulting in better service for you and those with you.