Startup COO job boils down to this:
1. Pick a problem area, and build 0 to 1 yourself. First principles get you pretty far!
2. After it gets going, start recruiting for an experienced leader for the area.
3. Onboard the leader well, nuke yourself out and attack next problem.
When startups start taking off, the founders usually can't tell what's changed. It's some combination of all the random things they did to make it take off, but it's hard to say which ones.