I guess I'm lucky with good genetics, but a few things I have noticed.
When I eat my normal, healthy diet and stay super hydrated, my vascularity is pretty minimal (except when at the gym).
If I'm up for showing off a bit when I go out, I will carb up a bit. Also, a few strong drinks really seem to make them blood vessels jump out. Agree with the arginine...also helps. Staying warm seems to also help. When I'm feeling chilly, you can't see a thing, but when I'm feeling warm its a whole different story.
Good luck!