Pack light. The lighter you pack, the better your trip. Try not to take more than 2 bags for each person. Some are able to pack in only a carry-on and a smaller tote which is ideal. This eliminates the hassle and wait of checking a bag. Baggage restrictions are fluid--be sure to check with your airline for the current guidelines..
Plan your wardrobe. Try to mix and match your outfits using a combination of basic items to free up space. Shoes are major space consumers, so keep it to only a pair or two in addition to the pair you wear on travel day. Keeping a list in your suitcase will make your packing easier the next time around and will be helpful if your items are lost or stolen. Know the weather conditions and culture of your destination and bring the appropriate clothing. You can also take old clothes and throw them out during your trip, effectively freeing up space to bring back purchases and gifts.
Go miniature. Try to use miniature toiletry items and appliances to free up space and reduce weight. Consider having a toiletry bag packed and ready to go at all times to make it easy. Do not fill your bottles to the top, and store them in plastic zipper bags to prevent leakage if they expand at high altitudes.
Pack tight. This gives you more space and less wrinkles. Roll your t-shirts and other casual items. Eagle Creek's Pack-It folders are helpful for compressing clothes and reducing wrinkles. Plastic garment bags from the dry cleaners also help reduce wrinkles for any garment you pack. Store socks and underwear in your shoes to free up space and reduce crushing. If at all possible, don't overpack! A regularly overstuffed suitcase will wear out faster than one that's been packed properly.
Always carry-on. Take any valuables, jewelry, cameras, medication, money, keys, documents, and a change of clothes in case your checked bags are damaged, lost, or stolen. Check Airline Carry On Size Restrictions.
Identify your luggage. Use an exterior ID tag (preferably one that keeps your personal information obscured) and another inside your luggage.
Remove old claim checks. This will avoid confusion for baggage handlers.
Insurance. Insure any valuables not covered normally by the airlines or common carrier.
Lock your luggage. This prevents accidental opening and deters theft. Traditional luggage locks are always a reliable choice, but you may also use plastic zip ties, which are available at any hardware store. Using a luggage strap is highly recommended for larger pieces (26" and up). This will also prevent accidental opening, deter theft, and help identify your luggage at the baggage claim.
Remove any detachables. Take off shoulder straps, hooks, add-a-bag straps, etc. These items can easily be lost, broken, or damage your suitcase during transit.