USE ONE CALENDAR.
The biggest mistake people make when using planning calendars is to keep more than one. Keep personal, professional and family items on one calendar. It will help to eliminate scheduling conflicts. Remember, 'the man who wears two watches, never knows the correct time.' This is a big one and one of the most useful. I keep my calendar, the events for three businesses, our family, Dave, and Mason. I use different color pens on my most organized day.
The only exception to this rule is I keep an on line calendar for Dave, Mason, me, and our family events. Doing this means I have to put it on line after I put it in my book, but this way, Dave has a point of reference when he needs to schedule something and can't reach me.