After hooking up to city water (after de-winterizing & all season long), I always open hot & cold faucets until they stop spitting & hissing air and there's a steady flow of water coming out, then the heater gets turned on. We never use the water heater on electric and have it turned off at the heater so it will never accidentally get turned on if the tank is dry. If the tank was empty, it takes a bit to fill up and you can hear it filling up (at least I can) and while it's filling, you'll only get air out of the faucets.
If you have a 30 amp TT, the electric element will take up about 1/2 of your available power. Unless you are wanting to make a CG pay to heat your water or need to conserve propane, run it on propane. It's much faster anyway. Electric and propane can be used together if you want faster recovery. An electric element will burn out in seconds without water in the tank.
One thing not to do is to open the pressure relief valve after the heater has been turned on to avoid getting scalded.
Did the dealer not demonstrate how to winterize & de-winterize? When the time comes this fall, you can winterize with either compressed air or RV anti-freeze. Another thing to know is that there's two types of anti-freeze and the propylene glycol type is a much better choice. Also, there's "low point" drains underneath to drain water out of the lines. At the end of each season, you should inspect the anode rod for erosion and replace when de-winterizing if needed. Keep a spare on hand.
BTW, remember to turn the heater off while parked at home so you're not wasting propane or possibly using it up.
I discovered by accident while in Las Vegas (forgot to turn heater on) that you don't even need a water heater... Cool! :C