"We wish we had more top charities [...] there will need to be more recommended charities in order to productively use all the donations that GiveWell-influenced donors are making. One of our major activities is trying to expand our top charities list, both by investigating charities that already exist, and by supporting activities — from new nonprofits to studies — that could eventually result in a larger set of evidence-backed programs and a larger set of top charities." (Source)
To get started, check out GiveWell's past incubation grant recipients and their current priority programs. (You will also benefit from an understanding of the existing global poverty interventions that support GiveWell’s selection of top charities.)
Charity Entrepreneurship has taken GiveWell’s request for new charities seriously, conducting their own analysis of the priority program list and starting a charity to tackle one promising intervention. Contact them if you think you have the right mix of interest, skills, and willingness to acquire domain expertise. GiveWell, Charity Entrepreneurship, and many other sources will gladly fund you to do this work.