Being a good restaurant customer involves more than leaving a decent tip. It also means making the job easier for the person juggling your order, three other tables, a kitchen ticket, special requests, and possibly a customer who has decided that a booth is a constitutional right.
Restaurant servers work in a fast-moving environment where small customer choices can either keep things moving or create a surprising amount of extra work. Good manners matter, but so does awareness. A customer can treat a server politely and still make the shift unnecessarily difficult without realizing it.