Disclaimer: I'm just a first year student, so someone else on this board will likely have a more informed view of things. But we did finish a block on hemodynamic disorders in my path class a few weeks ago, so I'll take a stab at it:
--The mechanism by which smoking induces thrombosis is not known. One theory is that smoke products in the blood can cause damage to endothelial lining of the vasculature, which can predispose to thrombotic events (part of the "Virchow Triad")
--With oral contraception or hyperestrogenic states, it is believed that synthesis of certain coagulation factors by the liver is increased, thus upping the odds that the coagulation cascade will be set off, or that it will "over-react" to an endothelial insult.
Again, that's to the best of my still limited knowledge. Hope it helps.