Usually I open up Sai, then stare at the blank screen on my tablet for a few hours. Then I scribble randomly in the vague shape of what I want to draw, go cry and watch some youtube, come back, set the scribbles to low opacity and re-draw it on a new layer, then repeat the process about 4 times, then trace it on a vector layer for smoothness, color it, then shade/highlight it.
Oh and listen to some music. It helps with developing a more productive mood and drowning out the crippling thoughts of self-doubt. :D