1. You don't arrive on time

"It drives [some] doctors crazy when patients turn up late for an appointment," says Mary Catherine Beach, M.D., of the Johns Hopkins School of Medicine. "You can see the irony in that because patients almost always have to wait to see their doctor." But quite often the reason you're left twiddling your thumbs is that someone who didn't arrive on time messed up the schedule. "If you come in late, I can almost guarantee that your doctor won't feel as happy toward you as if you'd been on time," she continues. Some doctors tolerate late arrivals better than others, but no one likes it.

Here's a tip: Ask for the the first appointment of the day, so you won't get caught up in other things before the appointment. This also works in the reverse — for doctors who always make you wait.