Since that does seem to be an organization issue in some homes I thought I would share my very simple tips in hopes that it might help somebody.
You will need: Paper (stationary and cards are fun "paper"), Envelopes (We like to get fancy and make our own most the time and I actually have little totes to keep all our cards and envelopes in and they "live" nearby the stationary folder), Stamps, A Pen, Addresses and Address labels.
For our address book we write addresses and phone numbers in pencil so that if they change we can just erase it and write in the update.
It has been very helpful to us to have a consistent place to keep our letter writing supplies and so we don't have any excuses besides lack of time for not getting letters sent.
How do you keep organized in this area?