Start the year out right... put EVERYTHING on a calendar. If you use an electronic one, I cannot help you, but it probably moves most repeating stuff like birthdays over. However, school years change and many districts already have a calendar up for next year.
I print out pages from printfree.com, hole-punch them and put them in a sturdy folder (with those metal thingys that I cannot think of the name of) so that I can have someplace to keep invitations, hand-outs from meetings or my notes about things I need to do. In fact, I love this folder/calendar so much that I actually bought a purse that would be wide enough to carry it when it is on its side! How's that for reasons why you need to buy a purse? The other thing about the print free pages is I can keep more than a year in the folder, both past and future, so I can look back on things or be prepared for the whole school year in August. I also have a calendar that hangs on the wall (that I bought and now need to find) so I can put quick things on until I find my calendar, or things we're counting down to, or BIG REMINDERS like of birthdays and such.
At the beginning of the year, I am overwhelmed by the list of changes I want to make so I was having a hard time choosing where to start. Then I almost double-booked myself for this weekend... seriously almost bought hockey tickets to be with two kids when the third is in the All-City Honor band and has a CONCERT at the EXACT SAME TIME! Sometimes I am such a loser. But on the upside, now I will sit down and put all birthdays, commitments, etc on the calendar this week.