My desk calendar is for me and my husband. Here is the information that goes into this calendar:
1. Medical appointments with the appointment card filed in the date of the appointment.
2. Invitations filed in the date of the party.
3. Bills that need to be paid are filed in the date that they are due.
4. Birthdays, anniversaries, etc. are written in the calendar.
5. Special cards that are bought ahead of time are filed on the day they are to be mailed.
6. My husband's work schedule is written in the calendar.
7. Any other important dates are written in the calendar.
My to do list is made off of this calendar, so I know exactly what needs to be done for the week ahead. It has never let me down and I have never missed paying a bill and never have I missed or double booked an appointment.
My daily planner calendar is used for all my work appointments. I carry this with me when I leave the house. I also transfer the important appointments from my desk calendar into here so I don't overlap appointments.
Finally, my phone calendar. I transfer work appointments and personal appointments into my phone. I rely on this calendar when I quickly need to glance at my schedule. I can pull it out at a moment's notice so I don't leave anybody waiting or tell them I have to call them back because I am not prepared.
If you are not using a calendar, I highly suggest you start using one. You don't have to use 3, this is what works for me. Buy a calendar that works for you and one that you know you will use. A calendar is a great way to start getting organized if you don't know where to begin.