For certain values of "success", neither...it is an internal psychological/spiritual state. For other values of "success", it is by definition arrived at only by hard work. For still others, a little of both. "Success" is a quintessentially ill-defined specification and since we don’t need to design to that specification, it should be ignored as a general rule. Most wise people deprecated the term a long time ago.

As someone that has endured a significant amount of bad luck, is there any advice on improving luck?

Little from column A, little from column B.