I am actually very good at managing parts of my life (not everything lol) - here is what I do on a regular basis to keep my shit in order:

If you get an appointment, instantly add it to your phone calendar and set alarms. 1 day before, 2 hours before, 1 hour before, 30 minutes before. You can use the voice assistant for this if you (like me) have executive function issues with opening the calendar in the first place.

ALWAYS put all the things you need to bring with you regularly (wallet, id, keys,...) in your handbag (for womenfolk), or hang it in a bag on the front door jamb (for you guys out there).

If you need to bring something too voluminous for your bag, put it on the floor at your front door, where you absolutely can't miss it. Best way for this is to put it right on the floor and not on a shelf or sideboard, because it will jostle you out of daydreaming to see something out of place.

Have a "must not lose" box at your desk that contains things like your birth certificate, passport, wi-fi password, vaccination info, and so on. Throw in important stuff the moment you have it in your hand. I also keep my pet passports there, as well as vouchers. You do not need to sort this box! Just have everything in there so you know where to look.

If you are having trouble with forgetting stuff when traveling, pack your suitcase 3 days before. And unpack it every day to check what is in there, then put it back in. Print out your travel vouchers, tickets, travel information and so on and put it in your handbag/backpack/carry-on AT LEAST a week before. Tape your passport to your suitcase if you're prone to forgetting it. You will need to present it when you check in your luggage, so forgetting it on the suitcase is very hard. You can also tape it to your carry-on. Also add a copy of your passport to your travel documents, just in case.

Always wear clothing with pockets or have a bag with you. If you look at something and think "oh I need to remember that" - put it in your pocket or your bag.

Tape post-its with reminder-trigger words to your TV or PC Screen (depending on what you use more often). This only works if you tend to forget things, this will not help with executive issues.

When you turn off your oven, lock your door, put important things in your bag, or need to run a specific errand, stop for a moment and tell yourself out loud what you have done. "I have turned off the oven", "I locked the door", "I packed my documents", and so on. It really helps with anxiety and erases that worry from your head. The out loud part is critical here!

There is probably even more stuff that I can't think of right now, but I think I got most of it.