Guidebooks invariably do a terrible job of explaining US tipping. They try to handle every possible nuance, when a tourist can ignore 90% of that. They should just focus on "how do you tip so that people don't yell at you."
And my version of that is:
* Tip 20% at restaurants if you have a waitress.
* Round taxis up to the nearest $5.
* If someone handles your bag or car, give them a $1.
If you don't know the rules of tipping, and when to break them, just pay 15% at a full-service restaurant, and 10% for cabs, deliveries, and buffets. Don't tip for walk-up counter service.
Tips for other services should be based on what you would be paid at your job for the amount of time they are saving you, with a minimum of $1. If you would prefer not to tip the valet, park your own car.
If your service was more than a standard deviation better than the median, pay more. If it was more than a standard deviation worse, pay less. You shouldn't pay 0% without also considering a complaint to the management.
And my version of that is:
* Tip 20% at restaurants if you have a waitress.
* Round taxis up to the nearest $5.
* If someone handles your bag or car, give them a $1.