I get paid to help people be more organised. Seriously. It's what I do for a living. I am a naturally organised person but I work with people who are nothing like me.
The biggest mistake people make is that they try to use someone else's system. What really works is a system that works for you. One that is designed for you.
Firstly think about how you function. Are you a visual person? Do you need to see lists or can you cope if they're in a notebook? Do big lists put you off? Would you be better with smaller lists of similar things like things to do with finance, errands, phone calls to make? Then you could have a daily list of a few things taken from the other lists. Some people I've worked with have set up a job diary instead of lists and write things in on a specific date.
Who else needs to be involved with your system? No point having a perfect planner / diary if it lives in your bag and your OH can't use it as well.
How much space do you have? Are you using it wisely?
Do you have a routine (shift workers are often the hardest to organise)? If so you can do a job of the day or job of the month system.
I'd also recommend timing how long things take you. This allows you to make the most of the time you have. So if I'm going out in 15 minutes I know that I could empty the dishwasher (5minutes) and change a single bed (10 minutes). Voila two jobs done in time that might otherwise have been wasted.
I also try to make time count for double. So if I go into another room think what else needs to be taken there and do that at the same time. Try never to go anywhere empty handed. Do two jobs at the same time when you can. Cook two meals at a time etc.
Plan plan plan. I spend an hour each Sunday night planning meals, lifts, childcare favours etc for the month ahead. I get swimming kits / dance kits/ musical instruments ready then for the week ahead. They go on hooks on the doors in the children's bedrooms.
Get everything ready the night before. I put clothes out including underwear and accessories and change my handbag if I need to. I check my diary and family planner the night before and everything we need is assembled in the hall before bedtime. I leave my diary open on my bedside table to remind me.
My children have laminated checklists stuck to the fridge. No TV until all items are ticked off.
If paperwork is a struggle keep a box with pen, stamps etc by the front door and do it when you check the post. Could you make a little desk for yourself and have an intray if that would work for you? I use a bring forward system for remembering things and I have a reminder on my phone to check it every evening.
Sorry I seem to have done a bit if a head dump and this is long. I hope some of it is helpful. Happy to answer specific questions if you have them.