Once upon a time, trenching around your tent to divert rainwater was standard procedure. We all know better now, thanks to the LNT (Leave No Trench...er, Trace) folks. But you can still drain rain away from a less-than-ideal tent site by building a rain dam.
Line up 1- to 2-inch-diameter sticks or stones to create a ridge. Anchor the edge of your ground cloth under this ridge and then pitch the tent with its edge atop the ridge.
A properly built dam will direct runoff away from the tent and prevent water from being trapped between the ground cloth and tent floor. When breaking camp in the morning, scatter the building materials, and remember, leave no trace.