A high school principal posted recently that he wanted to set up a system using index cards. Here were my suggestions based on the specific needs he was looking for. Hope this is helpful:
I am an elementary school principal, so I know what you mean by having lots come your way. Back in February, someone was wanting to implement a system based on index cards and was looking for suggestions. Posted below was my suggestion. As far as how to keep from having a "to-do" list, I suggest separating your index cards by the context for the next action. All of the cards where a phone call is the next action go in one stack, those where the next action is something you have to do out in the building in one stack, etc.
Here is one way you could structure a system with nothing but 3X5 cards:
1. Have an index card for each project (instead of each task). Write the name of the project at the bottom of the card phrased in such a way that you will know when you have completed the project.
2. On the top line of the card, write the next action.
3. If you know what the NEXT next actions will be, continue listing them on the card one underneath the other.
4. As you complete a next action, highlight it with a highlighter and make sure you have at least one next action listed below it.
5. Use the back of the card to make notes regarding details of phone calls, confirmation numbers, and other info related to the project.
6. Organize your cards by context. All cards where a phone call is the next action will be sorted together, all cards where an errand is the next action will be sorted together, etc. You could put a rubber band or paper clip around each context.
You will be "done" with a card when the project has been completed. In other words, you have accomplished the last line on the card. The card will contain all of the next actions that led up to the completion of the project (you could even date the next actions as you complete them). All of your miscellaneous info will be on the back. You may want to keep a 3X5 file box of your completed projects.
This is just a thought of the top of my head. Hope it helps.