How do you prevent abnormal blood clotting?

Vitamins: The clotting system is very well self-regulated; there is little you can do to change it. About the only thing that matters is that some clotting factors depend on the presence of vitamin k in the diet; if there isn't enough, the production of clotting factors will go down, and your blood won't clot normally. That's how Coumadin (warfarin) works - it interferes with the function of vitamin k.