Your body is pretty much a zero sum game- a gain in one place means a loss in another. Every system is so intertwined, taking any sort of supplement (drug) would probably really mess something else up (especially where your reproductive tract is involved). Think of your biochemistry like a complex mechanical clock- if you change the way the one gear moves, the other gears will be affected, and all the hands will move differently.
That said, one of the first things your body does when you're having health issues is
shut off semen production. It probably makes for healthier offspring- sick stinkapes don't reproduce.
Your max production is probably around 2 tsp a shot. Next to keeping your brain fed, making sperm is the most taxing thing your body does. A lot of people eat low quality fruits and vegetables, so taking micronutrient supplements might help with the nutritious diet issue. (Re: Zn comment)
So my guess is that the standard 'stay healthy' mantra would put your semen production at its maximum:
- drink 4-8 glasses of water a day
- eat a nutrious diet
- get enough sleep
- exercise regularily
- drink less than five servings of alcohol a month
- stay away from other recreational drugs, including caffeine & tobacco
If you have recently had a health issue that's affected semen production, it'll take around ninety days for it to recover.
P.S. Movies are fantasy- you shouldn't expect to be able to reproduce Peter North's exploits any more than you'd be able to take a train to Hogwarts. Although I do have to admit, all the women I know have screaming orgasms just like Teri Weigel when I just touch them.
