• You do not need to wear something different everyday, you do need to be comfortable and appropriate: With that in mind, I use a packing formula: 3 bottoms for 1 week, 3 tops per bottom, 5 bottoms for 2 weeks, deduct 1 top and 1 bottom for each dress. True, that is not a lot of clothes but unless I am attending fashion week in Paris (hasn't happened yet), I can wear the same thing a few times.
• If you are going sightseeing or to a city, always, even in the heat of the summer, bring a cardigan (women) or a dinner jacket (men). I too vividly remember, as a child, my mother being asked to leave the Duomo in Milan because her arms were bare. Plus it comes in handy on a chilly plane. On that same trip, my brother had to borrow a dinner jacket at a restaurant. Not every place in the world is as informal as the States. On that same note, I always pack one thing I can dress up.
• Unless you are going to Antarctica or camping, there will be stores where you are going and you can always get what you need or forgot there. Apart from contact lenses or prescription medicine, you will be able to buy it at your destination. And, if you're in a foreign country, the replacement product will likely be more interesting than what you're used to.
• Forget the pack flat or roll debate. Bundling is best: I used to roll my clothes until Gregory discovered this method. Not only is it a space saver, it is genius at keeping your clothes from wrinkling.
• Pack one space saver bag: Just in case you buy a lot while you're away, the space bag may help you avoid having to buy an extra piece of luggage to bring it all back in.
Image: David Masters, from his Flickr, with a Creative Commons License, some rights reserved.