A while ago I read "Getting Things: Done The Art of Stress-Free Productivity" by David Allen, it was pretty good but I just combined it with Bullet Journalling and it's even better.
Key Takeaways from Getting Things Done:
1) Have one big 'To Do' list which you can add to quickly and you have access to it at all times. I was using the list apps Clear, and OurGroceries (this can be used for more than groceries), and a Calendar app. Take as long as it takes to compile all the on to do lists you have on the go. The idea of this list is to get things out of your head so they don't take up your mental bandwidth, cause you stress, and to prevent you from forgetting about them. You can delete them off your list if you want, but that is intentional compared to just forgetting. This can take a while to get set up, but try to power through and do it all before moving on to trying to do the things on the list.
2) As new things come in, if you can do it in 2 min or less, just do it. If you can't, put it on a list. If you need to make notes on it, have a stack of file folders, give each new item it's own file folder, and it's own hanging file. He didn't really get into electronic file keeping. I've almost adopted this at work, I'm certainly using more file folders than I used to.
3) Those first two are all I remember for sure, aside from those it is helpful to plan a time when you're going to do the things on the to do list rather than hope you find the time.
So I tried to have one master to do list but it wasn't working, and I had a separate notebook for each project I was working on. It wasn't working, then I saw a video on Bullet Journalling. It's pretty basic, but I think that's why it works.
Take any book (I'm using a 3 ring binder with lined paper), and add these pages
Index - self explanatory
Future Log - divide a double spread into 6 sections for the next 6 months. List significant dates or specific tasks you'll push out to those months.
Days of the Month Page for the current month - list the days down the margin, write in significant days.
On the opposite page write out a task list (kind of the master to do list to pick from if you can fit it there).
Then a double spread for daily entries - as you go write the day of the week, write what you want to accomplish or what you did accomplish or any little note. If you don't get to something you can move it to the next day or just cancel it.
After that make Collections - these are anything that hasn't fit in so far, books to read, places to go, food to try, etc.
I'm a week in and I find it much nicer to have all the collections in one indexed journal rather than separate binders. I think I'm making way too many collections but I feel free to experiment because it is a 3-ring binder.
Here are two links I found helpful, and the video I used to get started.