I like their framework of looking for cause areas that are large (you're already looking for this), tractable (so your work might actually result in something), and neglected (where your marginal impact is highest). That'll probably lead you toward:
1) Global poverty & public health: The evidence here is vast, and the marginal impact is huge in the developing world, where simple interventions like giving people money (GiveDirectly) or anti-malarial bednets (Against Malaria Foundation) save a life at the cost of ~$2,000. GiveWell does an excellent job evaluating these charities. This is where I ended up, but in the for-profit sector, at Zipline (flyzipline.com). We deliver essential medicines and vaccines by drone to the rural poor in Rwanda & Ghana. Some of our projects are funded by great organizations in this space like Gates & GAVI. I also donate ~50% of my income to GiveWell top charities, along with...
2) Farm animal welfare: Depending on how much you value an animal's life and well-being in relation to a person, the vast suffering of farmed animals is a huge problem that is also quite neglected and tractable. According to Animal Charity Evaluators (the GiveWell of this space), the most effective organizations are those like The Humane League (corporate outreach for improved standards) or The Good Food Institute (promoting and developing meat-alternatives, e.g. Impossible Burgers, or cultured meat).
3) Improving the long-term future: If you value the lives of future generations, then you might choose to focus on mitigating existential risks, i.e. those that risk extincting humanity. AI risk mitigation, e.g. OpenAI, gets a lot of focus in the bay area for obvious reasons, but there are many other opportunities here, e.g. reducing global pandemic risk, nuclear security, etc.
Hope this helps, and of course, I'd be happy to provide more links, articles, books, blogs, or podcasts on any of this! Or even better, put you in touch with some of the folks who work at these organizations