I keep my seeds in a box with seperate casettes in it. I organize by month. Works quite well for my brain.
I have a plan in the beginning of the year, abandon that, roughly outline a new plan and then whenever there's about to be an empty space in my garden when I'm about to harvest something, I have a look at the month to see what else I can sow to fill up the empty space.
At the end of the month, I go through the seed packets of that month, move the seeds that still can be sowed next month to next months casette and work from there. At the end of the year, I reorganize, see what's to old, what's missing for next season. Then I go and buy to many new seeds and stock up again.
I have a box for veggies and fruit and a box for flowers. Struggling with my peas and beans though, they don't always fit. I might need another legumes storage solution.
I poorly keep track of what I'm sowing when and what the harvest is like, in an old-school paper agenda. I store what I like in my head. Not quite happy with that system, it's not always very reliable.