If it's the first time this trailer has been hooked up to "city" water, after you turn the water on look around for leaks. Our Safari had a loose connection in the bathroom, and after a few minutes we saw water on the floor. No more fresh water that weekend! Bring along a couple of jugs in case that happens to you.
Then turn on the hot water so the water heater tank can fill up.
Also, bring a couple of white hoses for connecting. On some campsites the water connection might be 20 feet or more from your hookup.
And be sure to connect the source to the water hookup, not the black tank cleanout hookup. On our Safari the black tank cleanout has a sign on it and is to the right of the fresh water input.