Most of my family is from here, so I’ve been through the country a few times now. Most of the locals speak English fairly well, so there’s not much to worry about. As with any country, it’s always a compliment if you learn at least some of the language.
If you’re checking out the Red Light District in Amsterdam be sure to stick to the populated areas, otherwise you might find yourself in an unpleasant situation. You’ll know you’re in the bad/worse section when there’s almost literally no one and you’re surrounded by dull grey buildings rather than the flashy sex shops and Chinese restaurants. It’s also imperative that you don’t take photos of the prostitutes on that stretch because you will have at least your camera broken.
Some other fun (local) places to visit are the market in Emeloord, the northern part of Giethoorn (it has no roads, just canals), and the Efteling even if you’re not with kids.
Also, be sure to stop at a local restaurant to try krokets and pannenkoeken (pancakes, but yummier than their North American counterparts).