Make a packing list. Write down everything you know or think you'll need. Include the obvious basics, like underwear and hair products, and the not-so-obvious miscellaneous items, like a small house-warming gift for your hosts.
Be realistic and critical. Once your "what to pack" list is done, review it with a critical eye. Depending on your destination -- a friend's house or a hotel, for instance -- certain items can be omitted, like towels, or washcloths. If you noticed you wrote down "sandals" along with "flip flops" and "summer flats," narrow this down to just one pair.
Minimize your containers. Transfer big bottles of shampoos and body washes into the smaller, travel-friendly versions. This saves tons of space when packing your bath items. This can work with other items, like gels or body lotions.
Pare down the clothing. It's tempting to bring a variety of outfits to choose from for every possible situation, but strict selection here will save lots of space. Bring only enough clothes for one outfit per day, if you won't have access to a washer or dryer. If you will be able to wash your clothes at least once, bring 5 outfits and wear them each twice. To save even more space, bring only one or two pairs of pants and use these throughout the duration of the trip.
Keep your destination in mind. There's no need to bring pairs of shorts for your winter skiing trip, or to lug along the parka for your beach getaway. By eliminating the "just in case" items, your suitcase will suddenly have more breathing room. If you're going to a location with mixed climates - cooler at night and hot during the day - bring only the most spartan selection of heavy clothing.
