It is really easy if you look up an electron configuration table (one that looks like a periodic table) and then just go down the rows left to right, top to bottom, and just stop when you get to where the element is on the table.
[tex]1s^2 2s^2 2p^{6} 3s^2 3p^6 4s^2 3d^1^0 4p^3[/tex]
