First, you have to get a very, very low body fat percentage (Around 6% for men). Then, you have to get ripped by lifting a lot of weights. At that point, it is mostly up to genetics whether your veins will permanently pop out or not.
Before competitions, body builders eat a lot of sugar which makes your veins and arteries enlarge and pop out for a short time.
leave you arms hanging there and the blood flow builds up there or take one hand and rap it around you other arm and squeez it tight then with your free hand rapidly move them around and they might come up then
I would think it has to do with how thick or thin you are, but try holding heavy objects like sandbags or weights in both hands for awhile and that should give them that protruding look.
When I was a young man I wanted the same thing. It makes you look tough, your blood is pumping heavy.
The way to have it happen is to work out and work out hard. You don't want your veins visible to people or yourself though, be happy you can't see them.