Hello Eunice Gates,
On land you will want to do full body strength workouts; do not skip the push ups. Jump rope will help stamina. Remember to stretch the entire body, also.
In the water, incorporate all the strokes, the butterfly stroke requires more energy. Also, swim as long as possible without taking a breath by doing sprints, if you will. Swim using only the arms, swim only using the legs. If you swim in a pool, do the flip turn.
Do you specialize in a stroke? If so, practice that stroke.
Have fun swimming.