Focusing on efficient strokes will help you reduce the amount of effort it takes to get from one end of the pool to the other. Use the distance per stroke (DPS) laps to get your stroke count down as low as you can. Aim for under 15 strokes for beginners, less than 10 for more advanced swimmers.
4x25s kick @:20 seconds rest
6x25s DPS Freestyle @:20 seconds rest
(try to reduce your stroke count on each lap)
4x25s Sprint @:30 seconds rest
(as fast as you can go while maintaining stroke technique, reduce time by 2 seconds on each lap)
2x25s easy cool down.