Learn to let go
You know those two boxes full of assorted crap you haven’t unpacked since the last move? Throw them out. Don’t even open them, just toss them right in the trash and save yourself the two hours of agonizing over whether you can really part with that mini screwdriver/flashlight combo someone gave you that might come in handy one day, like if you had to defuse a very small bomb in the dark, or something, you never know, right? If you didn’t open them in the last two years, you don’t need what’s inside. Make your move easier -- and your new place more spacious -- by using each move as an opportunity to clean house. Literally.
Don’t be a macho idiot
No, you cannot empty your entire bookshelf into one giant box and carry it down three flights of stairs. And if you do manage it, that’s going to be you done for the day -- maybe for the next month. Professional movers can do this because they have spines of iron and the stamina of a sexually adventurous racehorse. If this does not describe you, pack smaller.