A legal framework that enables the land you do have to be less like Atlanta and more like Paris.

Eliminate minimum requirements on parking and restrictions on height. Make demolitions easier. Eliminate the neighbors ability to stop any project that they don't like. Reduce the number of permits required, reduce the permit fees, reduce the time it takes to issue a permit.

In the case of San Francisco, they also need a centralized, online planning/permits database. They are still doing things on paper, and they've got a backlog of thousands of permits. It can take years and hundreds of thousands of dollars simply to navigate the permitting process.