Memorize Transition Metal Electronic Ground State In the course of my undergraduate studies it has become clearer and clearer that it is quite helpful to know the ground electronic state of transition metals by heart, if only to speed up the process of analysing a reaction or to evaluate a compound in respect to its number of valence electrons. 

Edit: Note that when I say ground electronic state, I don't mean the state in vacuum, but when the metal is bonding to ligands. As a consequence all the electrons are found in the $d$ orbitals.

My Method:
I have now put the $d$-Block of the periodic table as a wallpaper on my screen background so I get constantly exposed to the arrangement of the elements.

What is your way to memorize what metals have which $d^x$ ground state?
Wikipedia has a comprehensive list on chemistry mnemonics, with which I'm now memorizing the position of the transition metals.
For example, for the first two periods of the elements (excluding neon):

H He Li Be B C N O F
Ha. Healthy Little Beggar Boys Catching Newts Or Fish.

Or my favourite for the first period of transition metals:

Sc Ti V Cr Mn Fe Co Ni Cu Zn
Saint Thomas Very Carefully Made Five Completely New Copies of Zarathustha.