Obviously, packing light has many definitions for different people, but we definitely recommend a carry-on sized piece of luggage (even if you end up checking it).
A year of travel often comes with constant packing and unpacking. Packing organizers like packing cubes, compression sacks and even ziploc bags make the process way easier.
Look at the destinations you’re planning on visiting. Are they mostly warm weather or cold weather destinations? Pack a week’s worth of clothes that go with the climate where you’ll spend most of your time.
Pack versatile items that can be worn multiple ways, such as a scarf that can keep you warm in cold climates and worn as a sarong in warm climates.
Remember you can buy clothing all over the world. If the t-shirt you’ve been wearing twice a week for four months starts getting holes in it, you can buy another one to replace it.
Any trip longer than a week will require doing laundry, and that is certainly true if you’re traveling for a year. You don’t own a year’s worth of clothing, so you can’t pack that much anyway.