My general watering regime is 1/4 strength fertilizer at every watering during periods of active growth. Your mileage will vary depending on how much more than what kind. In other words choose a fertilizer that is balanced (nothing special required for succulents) but measure it so you don't overdose the plants. You can save the leftovers for the next watering, just leave them in a closet or a dark place.
Be sure you flush some water out the bottom every time if possible so that the salt does not get out of hand.
Another related issue is the pH of your water, which may be close to neutral and just fine... but our tap water is groundwater and it comes out at pH 9 or so, which is quite alkaline. The plants are much better able to make use of nutrients when the water is neutral or slightly acid. So I acidify the water that I use for my plants (using aquarium chemicals, not rocket science), and they thank me for it.
