i think alot of it is genetic...im 6'1 255 lbs with around 10% BF. a little veiny in my arms during workout but thats it. when on gear im a bit more vascular but not much. got a budy thats never taken anything and weights around 170
hes got huge veins coming out from everywhere, especially when he works out. low bf, but doesnt eat reall well or anything. great genes though