Do not be tempted to rent a car. There is no place to park it. Parking fines can exceed $100. Amsterdam police know all about how to use a Denver boot. There is no place in the city you cannot reach on foot if you are reasonably healthy.
Amsterdam is not easily accessible for the handicapped. The upper floors of these old buildings are reached by narrow, steep and curved flights of stairs. Newer hotels do have elevators, as do some of the museums. Do check carefully before you go if this could be a problem.
Signs warn visitors about pickpockets. Your best defense is your brain. I don't care where you are going, leave good jewelry and other conspicuous valuables at home. Are you interested in expanding your mental horizons or impressing the natives with your wealth?
Carry only what money you will need that day. Leave the rest in the hotel safe. U.S. credit cards work as well in Amsterdam as they do in Washington.
I did not feel at all physically threatened in Amsterdam, even when I found myself surrounded by a group of very drunk young men celebrating a soccer victory late one night.
Wear flat shoes with a cushioned sole. Streets and walkways are cobblestone and an invitation to broken bones for anyone wearing high heels. The cobblestones were the only hazard to health to be found in Amsterdam (unless you count what all that cheese can do to your cholesterol).
Take a raincoat and water-resistant headgear. It can rain at any time, but never for long. A real downpour occurs only occasionally. Retreat to a shop and have some coffee or hot chocolate until it ends. Any excuse is a good excuse for Amsterdam's coffee or hot chocolate.
Dress is casual. A crowd on an Amsterdam street looks just like a crowd near Dupont Circle.
The Dutch are lovely people with polite manners. Do leave them with the impression that the same things can be said about Americans.
And, yes, you can drink the water. What comes out of the tap is far superior to what is served up in the District. The Dutch don't stand for any nonsense from water - wherever it is found.