Ordering alcohol on a first date signals nervousness to her

If you order a drink right away just to calm your nerves, it signals two bad things at once: that you are nervous, and that you need alcohol to talk to women. Both are unattractive qualities. The opposite extreme is equally problematic. If she orders a drink and you decline with "I don't drink," you can come across as the guy who doesn't know how to have fun. The middle ground is to explain you drove and have things to handle afterward. That one line makes you seem busy and important, and it kills the issue entirely without either extreme.