What are the 3 rule the govern the filling of atomic orbitals by electrons?

Answer 1

1.I don't know how many rules you have been given but here are some.
a. Lowest n fills first
b. s before p before d
c. Hund's rule of maximum multiplicity(;i.e., don't pair electrons until the set of p,d,f, etc are at least filled.

There is some juggling that goes on for the b rule and sometimes some juggling for rule c.