I don't really do anything in particular before or while masturbating. I tend to just masturbate for the sake of the act itself and the sensation.
It's like if I have an itch, I scratch it (not that I masturbate as often as having an itch).
I suppose I don't really associate masturbating as a special erotic activity like actual sex or kinky roleplay. So there's no need to prep myself by doing something like look at porn or erotic images.
But when I do feel aroused as a result of some porn or sexy images, I am more likely to have the urge to masturbate afterwards.