Step 1: Determine the number of electrons to appear in the electron configuration.
Step 2: Add electrons to subshells in order of increasing subshell energy.
Step 3: Observe the Pauli exclusion principle. There can be no more than two electrons in an orbital, and they must have opposite spins
Step 4: Observe Hund’s rule. Orbitals in a subshell are singly occupied whenever possible. Also, all unpaired electrons have parallel spins.