I agree with sprint laps, good way to get your heart rate up, was kinda doing that for a while but was outta shape.
Good equipment to use:
Kick board to do a down and back a few times to get warmed up. or u just want to work kicks.
Hand paddles, to focus on shoulders and arms. upper body.
Flippers for legs.
When using paddles or fins, just focus on good form rather than speed, so u get best benefits.
Also, if u are not doing all the strokes, freestyle, back, breast, fly then you should. Or atleast learn them. and incorporate.