* Leave a tip for efficient service
I always thought part of the point of Uber was not having to deal with cash and tips. I've never left a tip for my driver, and never really had an opportunity to as it's all paid for by your credit card on file.However, I do most of the rest (never really thought of complementing anyone's car, they pretty much all run together to me), and have a 4.9. I never even thought about making smalltalk as a way to get your driver to rate you better; it's just a nice thing to do when you're getting a ride from someone.
One of the interesting things I've noticed about Uber is how diverse the drivers are. I've gotten (at least) Russian, Kurdish, Moroccan, and Nigerian drivers, so that's led to some interesting conversations about where they're from and what it's like. From the conversations, Morocco sounds like the best place to go visit; the guy from Morocco waxes the most poetic about his homeland.