Get really, absurdly good at something without regard for how long it takes. Then after that start probably fuck around for awhile and just do whatever I want (obviously will probably still have to work). Beyond that just normal life stuff like have a family, etc. Once that's done maybe recommit myself to working on extreme moonshot goals that would normally be out of reach during a normal human lifespan. Maybe try and understand how to further improve the intelligence of humans, space travel, etc.

If you're truly immortal though (accidents or violence notwithstanding), then eventually it would probably end in a medical suicide for most people at some point.