You do have a passport, right? It can take about 6 weeks to get one unless you pay for it to be rushed.
Get a guidebook (I like Let’s Go best for this) and look through it before you leave.
I generally don’t drive when I’m on vacation overseas- it’s just not terribly helpful to have a car to see the sights in most of the cities, parking would be a pain, and gas is much more expensive than it is here.
If you do drive, be aware that their drunk-driving laws are more stringent than ours- 0.05 instead of 0.08. Rick Steves recommends drinking only after you are done with all driving for the day, which I think is an excellent idea. If you’re going to smoke pot, don’t drive after doing that, either.
Weather forecasts are in centigrade. If you (like me) are used to Fahrenheit and can’t do the conversion in your head, this is generally close enough:
30 is hot
20 is nice
10 is cold
0 is ice
Don’t bother with traveler’s checks, and don’t exchange cash if you can help it. It’s much more convenient to get money at an ATM when you arrive at the airport (assuming that you have a 4-digit PIN). I haven’t been to the Netherlands, but in Britain, France, Italy, and Ireland I had no problems finding places that took credit cards. In Australia a lot of places had a minimum charge, though. You might want to let your credit card companies know you’ll be travelling- sometimes they see foreign charges and flag it as potential fraud, and you can’t use the card until you call them and straighten things out.
Not all hotels have private bathrooms in every room. You should ask beforehand if a room has an ensuite bathroom, if this is important to you. If you do stay in a hotel with a shared bathroom, a word of advice- there is a time and a place for hour-long showers, and a shared bathroom in a hotel isn’t one of them. Oh, and be sure to lock (not just close) the door when you are using a shared bathroom so no one barges in on you. I wouldn’t expect a bathtub in the bathroom, unless I were staying at a really fancy hotel (or Dutch hotel standards are very different from British/French/Irish/Italian standards).
If the Netherlands is like France, Ireland, and Italy, soft drinks will be much more expensive than wine or beer at most restaurants (and will come in much smaller portions than we’re used to, and don’t come with free refills). You might have to order “tap water” if you want what you’d get in an American restaurant if you asked for water- a lot of European restaurants will assume “water” means bottled mineral water. Bottled mineral water doesn’t taste anything like our bottled water.
If there are any foods you don’t like or don’t eat (if you’re a vegetarian, for example), learn the names of those foods in Dutch, so you can recognize them on a menu. A guidebook might help here. The translation of a menu entry doesn’t always have as much information as the original.
You’ll probably see a lot more people smoking there than you would here, and you’re less likely to be able to find a non-smoking hotel room. If you’re allergic to cigarette smoke (like me), be sure you have enough allergy medication to last through the trip.
Take comfortable shoes with you. You will probably be doing a lot more walking than you normally do, and that’s miserable when your feet hurt.