The student pilot was flying back to her home airport after completing a flight lesson with a certified instructor pilot (CFI). Prior to letting the CFI out of the airplane, the student verified that the right main fuel tank was active and full. About 700 feet above ground level, the engine began to sputter. The student pilot checked the ignition switch, and turned on the boost pump. She elected to land straight ahead into an empty field rather that attempt to turn back to the runway, and made a soft field power-off landing. During the landing roll, the right main landing gear began to sink into a furrow. This twisted the airplane; the nose gear collapsed, and the right main landing gear was bent. The student pilot was not injured. She stated that the fuel selector valve had been problematic due to its position and the lightness of the stop between the right main and the right wing tip positions. On previous occasions, she had noticed that it could be inadvertently moved from the right main to the tip, and had developed a method of planting her hand before selecting the right main so as to prevent the selector from moving through the stop to the right tip. After the accident, she verified that the fuel selector was in the right tip tank position, and that tank was empty.