Are you a note-taker like me? If so, try this organizational tip, which seems obvious to me, but which is fairly uncommon among lawyers in my experience.
For each case you're working on, use a separate notepad. Keep the notepad in the case file or in your desk drawer. Every time you work on the case--doing research, preparing for a hearing, etc.--use the notepad for taking notes, keeping the pages together in chronologically-dated entries.
If you're faithful to the system, you'll develop a date-ordered record of your work on the case, whether it spans months, years, or decades. This record will come in handy when you have to revisit an issue you already dealt with during the previous months or years.
When you get to the end of the notepad, label it "Smith v. Jones, Notepad 1," and start a new one. Due to the miracle of memory, you'll always associate particular issues you worked on with particular cases. If you save the notepads, you'll always have the results of your work at your fingertips.