What stragety did the continental army use in the battle of trenton and princeton?

The Continental Army crossed the Delaware River at night and surrounded the Hessian soldiers. The Hessians had lowered their guard believing that they were safe from any attack from the Continental Army because the Delaware River had frozen and they did not think anyone would dare cross it. However, the Continental Army managed to cross it and launched a surprise attack against the unsuspecting Hessians.