I'll be honest, first thing would be climbing on top of a skyscraper, blasting 'Princes of the Universe' from the top with a big-ass PA, then jumping down, splattering the sidewalk, then calmly getting up and walking away without saying another word.
"I AM IMMORTAL, I HAVE INSIDE ME BLOOD OF KINGS!"
From then on it'd be investing and other long-term plans of making money combined with, I dunno, getting a medical or biological degree so I can study my power and perhaps reproduce it in a synthesized form.
Of course it would not be to the extent of my immortality. I'm not dooming people to that, plus it'd create way too many problems to be worth the trouble.
Then once I engineer 'Eternal-life-in-a-can', I'll make sure it works for a limited amount of time, then make it available for an actually affordable price, both creating a monopoly on the product, which ensures sales, and avoiding the otherwise inevitable uprising of everyone who DOESN'T have millions of dollars for every dose, instead going for something more similar to a "10 bucks a month" plan.
If I get everyone in the first world on that, that's still billions every month.
Then once I have the capital for it, I'll buy out some major corporations, but capable folk in charge of them, and retire to my custom-tailored mansion to start working on spaceflight and terraforming the less habitable regions of the world, all research and staff funded by the above mentioned massive sources of income (Hell, I'll deny my own salary bonuses for the corporation positions. Free PR!).
Also, booze & blow. And other assorted hedonism that is within the realms of legality. Because just because I'm immortal doesn't mean I have to turn into a perverted creep, now does it?
My Science brings all the boys and girls to my yard.......