In general, when referring to a date without a year, there are two common approaches
the 12th of July
In general, when referring to a weekday without further modifier, the is not used
I will see you on Monday.
I need that report by Monday.
However, when you are referring to a particular day of the week, but indicating which one of the many possible instances of that day by adding a modifying phrase, the often (but not always) precedes the day
I will see you on the Monday after next.
I will see you on the first Monday of every month.
When you combine a reference to a date with a reference to the weekday that date falls on, the weekday is not usually further defined, so
I will see you on Monday, July 12th.
I Will see you on Monday, the 12th of July.