Two angles to answering your 2nd question:
One, how do you ensure what you write down is useful to your future self?
Two, how do you make sure you find it when and where you need it?
To ensure your future notes are useful to you, read what you have already written weeks or months (or more!) ago. Initially, I found my writing was too sparse. Too much context stayed in my head and my notes were almost useless. I reviewed them just before I completely forgot the context and updated them. The feedback loop of reading my own writing has helped me improve a lot at writing well for future me. I have to write to myself as if I will be an amnesiac in the future.
As for finding my writing when and where I need it, I try to give every file a unique and memorable title so I can refer to it in other notes and writings I access more frequently. For me, this means linking to notes and thoughts in Obsidian and creating aliases. If I know I wrote something down, but think the title is "Note B", but the title is "Note A", when I find Note A, I will add an alias with an additional title or keyword so that in the future, searching for Note B will surface Note A (and Note B, if it exists). Or, I will add a link to Note from the 1 or more of the most topically relevant note.
P.S. This maintenance doesn't take me much time. I only do it if I notice that a note was harder to find than it should have been and it usually only takes a few seconds to make sure it's easier next time.
(I used to use OneNote and Evernote, but bi-directional links with auto-suggest and a file quickswitcher are such gamechangers.
I was there when Obsidian and Roam Research felt like the first two options doing this seriously. The ecosystem has grown up around me and I love it. But you can do this with loads of other tools now.)
My filenames generally follow a "YYYY_MM_DD_HHmm Descriptive Title, perhaps a thesis statement - Source, if applicable" format.
To ensure your future notes are useful to you, read what you have already written weeks or months (or more!) ago. Initially, I found my writing was too sparse. Too much context stayed in my head and my notes were almost useless. I reviewed them just before I completely forgot the context and updated them. The feedback loop of reading my own writing has helped me improve a lot at writing well for future me. I have to write to myself as if I will be an amnesiac in the future.
As for finding my writing when and where I need it, I try to give every file a unique and memorable title so I can refer to it in other notes and writings I access more frequently. For me, this means linking to notes and thoughts in Obsidian and creating aliases. If I know I wrote something down, but think the title is "Note B", but the title is "Note A", when I find Note A, I will add an alias with an additional title or keyword so that in the future, searching for Note B will surface Note A (and Note B, if it exists). Or, I will add a link to Note from the 1 or more of the most topically relevant note.
P.S. This maintenance doesn't take me much time. I only do it if I notice that a note was harder to find than it should have been and it usually only takes a few seconds to make sure it's easier next time.
(I used to use OneNote and Evernote, but bi-directional links with auto-suggest and a file quickswitcher are such gamechangers.
I was there when Obsidian and Roam Research felt like the first two options doing this seriously. The ecosystem has grown up around me and I love it. But you can do this with loads of other tools now.)
My filenames generally follow a "YYYY_MM_DD_HHmm Descriptive Title, perhaps a thesis statement - Source, if applicable" format.