Be utilitarian. Make a list of what causes the most suffering and involuntary death, and personally contribute to work on whatever is high in the list and not being aggressively worked on today. Which is most of it. Degenerative aging and farming of animals, for example, being two things to eliminate on the time scale you mention. There is a lot on the list that can't be tackled meaningfully today, such as placing all higher animals into some form of simulation or at least controlled environments in which they can live as close to usual as possible without pain. Or means of human mind engineering to remove suffering without terrible side-effects. For that help to advance enabling technologies in the fields of computation, nanotechnology, and biology.