These are simple tips, but they have served me well all these years of packing light:
Think in layers. With clothes that can be layered, you can pack less and be warmer or cooler when needed.
Always have a “buy-it-there” money, so you can buy upon arrival the things you might need like shaving kit, etc. This money can serve too as emergency, when you need to buy a pair of pants because you spilled wine in the one an only pair you brought.
Take a minimal amount of toiletries. Buy the rest there and dump them before you return home (see previous).
Don’t use a wheely suitcase as carry on. Bring a backpack or duffel bag.
For your clothing, choose just three colors you look good in; make certain everything matches. Don’t worry about wearing the same outfit several times or more. Most people you encounter will see you only once.
Check the weather 1 day before your trip and pack accordingly. This will ensure you have the best options for the weather.
When you buy things, like presets or souvenirs, ship them home.
Make certain you have one comfortable pair of shoes that can be worn with most of the clothes you selected.
Take synthetic, wrinkle-free clothing.
Whenever possible, wash your underwear in the hotel/place you are staying. If you have the right underwear (syntheric), they will be dried overnight.
Think light on electrocnics. Do you really need a laptop, iPad, iPhone, ebook reader and camera?
Always pack a Booboo Kit or at least a minimal first aid kit.
Leave your oversized, thick wallet at home. Bring only the needed cards/ID and some cash. Leave all your coupons at home.