The effects of Safety In Numbers cannot be overstated. I’d go as far and say it’s even more important than cycling infrastructure like physically separate bike lanes. You do not want to be the only cyclist at a busy intersection between cars making a turn crossing your lane.

Might be counterintuitive, but if a helmet mandate reduces the number of riders even slightly it is a bad idea.

And of course: Wear a helmet. Especially if your city is still designed for cars.