Making the same 2 decisions before any trip I take has helped me pack lighter for years
I've traveled through Croatia, Greece, Spain, and beyond for upwards of 10 days at a time with one bag I can lift easily.
I know many people swear by rolling suitcases, but I like a carry-on I can stick under the seat in front of me that's never out of my sight - and the first time I tried to roll a suitcase uphill across cobblestones was the last.
If you ask me, packing light isn't about how tightly you roll your tee-shirts or sticking socks inside your shoes. Those tricks will only get you so far. To truly pack light, you have to make two decisions well before you head to the airport.
1. Know what you're wearing beforehand.
Sorry, but you can't bring "options." I never understand when people lugging a massive checked bag tell me they didn't "know what I'd feel like wearing!" You'll feel like wearing what you brought. Because those are your only clothes.
Chances are, you know most things about your trip before you go. If you know the approximate weather (it gets cold at night but you can go the beach during the day), the activities you'll undertake (hiking requires much sturdier footwear than drinking at a beachside cafe), and the level of formality of the places you'll visit (better cover your shoulders and knees in a historic cathedral) you'll know what types of clothing to bring.
There are a few nuances to this - having each individual item suit multiple outfits is invaluable - but you can plan every outfit you'll wear for the next week or so well before it's time to wear it, and avoid lugging unworn shoes across international waters.
In fact, by now, I have a few "travel uniforms" that I wear on trips to similar climates. Behold, from left to right: Mallorca 2015, Corsica 2016, Athens 2014.
I wore almost the exact same thing not only every trip pictured, but every day. Which leads me to the next decision to make ...
2. Accept that you'll wear everything more than once.
You can't have a different sweater for every night and a different pair of pants for every day if you want to keep things tight. I generally bring one sweater, one pair of pants, one scarf ... one of everything except shirts, socks, and underwear. For those, I bring half the number I'd need if I were going to wear a new one every day, and a little bottle of laundry detergent to get at least two days from each.
Again: Sorry.
If the idea of re-wearing socks you've hand-washed and air-dried in your hotel sink gives you hives (but come on), you can draw your own line. Maybe that line is staying in hotels with laundry service. You do you. But nothing saves space like jettisoning your backup jacket and "Tuesday" shoes.
I'll admit that a few things make this easier: I pack for one person. I don't have children and their space-hogging accoutrements. I'm not traveling for business, where you have to look freshly pressed at all times. And, although I've done otherwise, I prefer to travel during the summer to warm destinations - I'm not going to pretend I could cram skis into my carry-on.
But I've largely found that whether I'm headed to sunny Florida or rainy London, for three days or ten, these two decisions have made all the difference in packing light.