Default [Q] How do I theme Google Keyboard?

I am keen to be themer and was wondering how do I theme a keyboard for a start.

Here, Shaftamle had themed the Google Keyboard in various forms and I thought I would like to attempt to do up some themes too.

Can any kind soul advise me on how to start? Thanks!!
~Imagination is more important than knowledge~

Device: LG G2 D802 [Mahdi ROM 4.4.2] | Samsung Galaxy Nexus (Maguro) [CM11] | Samsung Galaxy S i9000 [SlimBean 4.2.1 w Semaphore Kernel]