Here's part one of my course on "How to pack light." No charge.
To begin, make a packing list. There are dozens on packing lists on the internet. Look at a few and write down anything you might consider taking on your trip. Don't think about packing light just yet. If you might want to take it write it down.
Once the list is complete, put it away and go do something else.
The next day, or a few days later, get the list and a pencil. Go through each item and ask yourself the following questions:
Will I use it? (If no, go on to the next item and cross it off your packing list. If yes, go on to the next few questions)
Will I use it enough to warrant carrying it for the entire trip?
If I need it, can I easily buy one at my destination? ( I quote I once heard was if I can get it within a few hours and it costs less than $20, leave it home.)
Am I just taking it for a "what if" situation?
Is there something better/smaller/more useful I could take instead that might do double duty?
Be tough on yourself. It's difficult to do the first go around. That's right, the first go around. You didn't think it would be that easy did you?
Put the list away. In a day or two, get everything on your list and spread it out where you can see them...the floor, a bed, a table, whatever. Pick up each item and ask yourself the above questions.
When you're done, and you may need another round or two, you will have your packing list.
Another key to packing light is laundry. Yes, if you want to pack light, you will have to do laundry. Figure out how many days worth of clothes you can manage with and make sure each piece mixes and matches with the others.
One thing to keep in mind......I'ts not finite. I've been a light traveler for over 30 years. I'm still learning as I go and I make changes along the way.