Hmm... interesting question!
If your planned retirement spending is less than you are spending now, it might help the transition to live on that smaller amount for these nine months.
Make sure your nestegg is firmly settled in your planned retirement asset allocation and that you have dotted all the i's and crossed the t's on your financial planning.
It might be helpful to get a physical exam from your doctor before retiring.
There have been several discussions here on when to give notice at work, and basically it all depends on your situation.
Gosh, I can't think of much that one should do during those last nine months, other than cross one more day off one's list every morning over coffee.