Keeping a good calendar is essential to your success as an assistant. Gone are the days when a big calendar on the wall would suffice. Now everyone needs access to everything from at least 3 different geographic areas and electronic devices, and it is up to you to make sure that people see what they need to see - and do not have access to the stuff that they don't!
In addition to all of these issues, you, yourself, will need an additional calendar full of personal information that you will need to use to sync up your own personal events with office work and projects. You may also be required to keep a similar calendar for your boss or assorted other parties in your office, depending on how in-depth your organizational responsibilities go.
There are several different takes on how to best handle calendar creation and maintenance. Here are some of the most popular. You will need to experiment to determine what works best for you and your employer:
Develop a Grand Monster Calendar
This calendar will have everything on it that you could ever need to know about anything. The benefits are that it centralizes all the information. However, you may have trouble finding information because the calendar is so crowded, and you will likely have to break this calendar down into individualized calendars for the individuals on the calendar, since it is unlikely that they all need access to each other's personal and professional schedules in detail.
Set up a series of individual calendars that you and the owners can both update
This is useful because it enables you and the other party to contribute to keeping the calendar current. However, you will end up spending a lot of time checking individual calendars to determine who can and cannot make events and you may end up missing items that have been updated recently or that an owner neither told you about nor added personally.
You can personally maintain "group calendars"
These are calendars of people grouped by association. This may be people with similar office responsibilities or who are parts of different teams but work together regularly. Generally these calendars should be maintained just by you so that people do not accidentally add or remove items that do not pertain to them. This somewhat eliminates cross-calendar checking, but it may mean that you also have to keep individual calendars so that not everyone in a group knows what every other person is up to at all times.