Some easy prep to do about 2-3 weeks ahead: Gather your camera accessories - charger and/or batteries, backup batteries, memory stick(s), carrier for spare memory stick. Now is the time to order a larger memory stick or a second battery.
One month before your trip - actually read your camera user's guide. Probably finding it will be a challenge, but most likely you can find the user's guide online through your camera manufacturer. Learn how to use the unique functions now. If you have a newer camera, some of the capabilities that may come in handy on your trip: GPS function; Delay function - so you can set up camera and run get in the picture yourself; Video.
Take an envelope to keep your receipts in. Briefly write on the receipt what it was - the day, when you were there (ie, wine at the café after the segway tour). When you get back home, it's hard to figure out all the charges on your credit card statement with the foreign names and you have no clue what they are. Having the receipts with descriptions will help you validate the charges.
Would you rather start your vacation aggravated and stressed out, or leisurely? Don't cut it close getting to the airport, or assume everything will go smoothly. Plan extra time in case there is a traffic accident on the road, a ridiculously long line for baggage check-in, and a back up at the security line. Give yourself plenty of time for all types of contingencies, and the worse that will happen is that you are bored because you have to wait a couple of hours for your flight because you cruised through check-in quickly. Compare that to the worse that can happen if you cut it close and then you hit a lot of snags - even if you end up on your flight, you will be anxious and stressed, and who wants to start their vacation like that?
When you travel, it is amazing how often you need change, small bills or Euro coins. A dollar here, a Euro there, particularly for tips or tolls, and usually you only have big bills from the ATM. So, prior to a trip in the US, use your large bills to pay for anything you can, and just keep all the ones and a decent amount of change so you are ready when you travel. If you are heading to Europe and you will get your Euros at the airport ATM, buy yourself a soft drink in the airport to break a large bill and get some change. As you go through your trip, use large bills as often as possible so you can get small bills and change, and only use your small currency when you really have to, such as tips. As my husband discovered, it's a bummer to tip 10 Euros because that is the smallest denomination you have.