What are some optimal municipal policies to address commercial property vacancies and develop vacant lots (among other issues addressed in the post)?

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A relative of mine is running for city council and is looking for optimal policies to address some specific issues:

1. Encouraging development of vacant lots. Not a lot of these but enough for it to be annoying. What generally works for this? Is zoning loosening the silver bullet for everything?

2. Decreasing vacancy in commercial real estate (store fronts and office parks mostly. Any combination of policies you all have found to work best for this or is it just another loosening of zoning thing to increase the potential value of the property?

3. Usual housing supply and affordability issues (I understand from reading many posts on this that it's just an issue of increasing supply by loosening zoning. There is a state mandate to create a specific number of affordable housing units that is difficult to comply with given current build out of the city plus strong political adversity to increasing supply and changing zoning. This is the question that I believe has largely been answered here and I know you can't answer the political issue and general NIMBYism.)

4. Curious about the efficacy of the second home tax in New York. This city has a large-ish number of second vacation homes that go unused or seldomly rented. Would ideally like to reduce this supply to go to permanent residents who would increase the tax base more.

Thanks for your help with this! They're trying to make this the best city possible.