Tbh I'm bad at this and I'm mostly writing it so I'll hold myself to it for the upcoming vacation, it’s largely geared towards not forgetting rather than over packing but repeating step 2 a few times could help
Make a List of everything you use on a more to less daily basis. (Toiletries, clothing, medication, but also phone, fidget toys, stuffed animals if they Bring You Joy, etc)
Separate into Human Essentials (includes Essentials for Proper Happiness and Function) and Additional Things I Enjoy but Can't/Don't Really Need to Bring (like an Xbox and flat screen TV or smth)
If there's any extra stuff you wouldn't usually use but will need on vacation, include them in your list now (Sunscreen, different types of clothing/ footwear, things like that)
Figure out how much space you have to bring your Essentials and if there's:
-too much, figure out how to (narrow down selection) stuff as many things into your bags and pockets as Possible
-extra space, you're probably good to go, or bring one or two Additionals (that will realistically fit on transportation)
If you can, ask someone to review your list and ask if there's anything that you've forgotten
Once you pack, keep a list of everything you've brought and check periodically throughout your trip that everything is there, (and if you need, include when and where you last reviewed inventory)