1. Lay out everything you want to take, and then take away a third of it. Are you really going to wear that shirt? Or are you just going to let it hang in your closet?
This will generate a lot of space.
2. Put your shoes on the bottom of the suitcase and place the shoes, heel to toe.
3. Stuff socks, undergarments, bikinis even in shoes. Wear your "bulkiest" shoes when traveling.
4. If you still have room, fill the gaps with t-shirts or pajamas.
5. If you have dresses or suits, stack them in opposite directions with the bottom half of the garment hanging out. When you're finished, stack them into a single pile.
6. Place a dry cleaner bag over the current clothes. The clothes will morph to the space allotted under the bag.
7. Place nice dress shirts on top of that, next to bagged toiletries (MAKE SURE YOUR TOILETRIES ARE SECURE, no one wants goopy clothes).
8. Try to make several outfits with a minimal amount of clothes.
9. If you don't have a baggage tag, try personalizing your luggage. I would recommend placing a strip of recognizable duct tape on it.
10. Make room! You can always go shopping!
Catch ya later, have a good one!