How to Get Life on a Lifeless Planet?

How do you get life on a lifeless planet? The fancy term for it is a biogenesis. We certainly know that there are organic molecules in astroids and comets. But getting the right chemical reactions to turn them from simple molecules to complex molecules is tricky. And these might be innovations in bi chemistry that might be quihte hard to find. You need to find ways of incoding that in your dna, or whatever the alien counterpart is.