1. Make a list
Start compiling your list right away. Use either the Sticky Note app or Google Docs (or whatever is easy for you) that you can keep open on your computer desktop all the time. Add to it as you think of more items. I even make notes by my bed right before going to sleep the night before a trip. If you take certain types of trips regularly (such as the beach or a cruise), you can use this list repeatedly, refining it every time.
2. Pack shoes first
Putting shoes at the bottom of your bag makes for better weight distribution. Packing them in cloth bags will keep them from getting your clothes dirty. Packing socks inside shoes can help prevent damage to shoes.
3. Sort your toiletries
I always bring some toiletries in my carry-on bag in case my checked bag is lost or delayed. Think through what your minimum needs would be if you had to spend the night without your checked bag. Also think about what creams and cosmetics are too valuable to lose in a checked bag. Separate these carry-on items into liquids and gels and dry items.
4. Prepare for the worst
Like I mentioned above, think about what you might need if you had to spend the night without your checked bag. In addition to toiletries, I always travel with a nightshirt and clean pairs of underwear and socks. Always include all prescription medications in your carry-on.
5. Lighten your load
You probably don’t need to carry everything that's in your everyday handbag. Carefully select only what you’ll be needing on your trip and leave the rest at home. Make sure your carry-on bags meet today's requirements. Airlines are becoming more and more strict about their carry-on limits.
6. Check your weight
Finding out your bag is over the usual 50 lb limit before you leave home is much better than being hit with an extra charge when you can do little about it. You can also buy a portable scale to be sure you aren't bringing home too much.
7. Know where you’re going
Of course have your flight information with you. Also be sure you have hotel and rental car information, contact information for anyone picking you up or giving you a place to stay. Share this information with someone not traveling with you in case you need to be reached in an emergency.