1. Buy the right suitcase.
I personally LOVE the suitcases that have zipper compartments for socks and underwear (and the pockets for shoes), it's like a quick hack for easy storage without even doing a thing.
2. Shove smaller things inside of shoes.
This is an easy way to keep valuables safe. I usually put my jewelry inside of a plastic bag and shove that inside of my tennis shoes.
3. Roll your clothes.
This is an old trick my mom taught me growing up. I not only use this in packing, but in my dressers at home. It makes things easier to get to when you're searching through your luggage, and makes everything just a little bit neater.
4. Ask yourself "Am I really going to wear this?"
Time after time I go on trips and have shirts I look at and I'm like "Why did I pack this.. I don't even really like this shirt.." There is nothing dumber than lugging around stuff you aren't even going to wear.
5. Leave room to bring back souvenirs
(Or bring an extra bag to carry souvenirs) Don't over-stuff your bag.
This is 10/10 the biggest mistake you can make when packing. ANTICIPATE
BRINGING THINGS BACK. Whenever I go on a trip, I usually almost leave
with new clothes or a souvenir of some kind.