New brake pads, cables, and modern compression less cable housing will go a long way increasing braking power. Look specifically for salmon colored Kool-Stop pads which will fit your existing brake calipers. They offer the best all weather braking power.

I would also recommend perhaps getting new Aero brake levers. The new style of levers provides better mechanical advantage and allow for adequate braking from the tops of the brake hoods. If you'd like the ability to brake from the flats of the bars, consider adding what are called interrupter brake levers.

A decent pair of fenders, Planet Bike/SKS (plastic) Velo-Orange (aluminum & stainless steel), would also be a wise investment.

Be sure to search the forum too. A lot of your questions are quite common and have detailed posts with pictures and explanations.