Try this fun workout as motivation to get back into the water after some time off. Each level has a technique or skill to focus on improving.

A (flip turns):
500 warm-up as 75 swim/25 kick on your back
16 x 25 on :30 (descend stroke count 1-4, 5-8, and so on)
8 x 50 on 1:05 (somersault in the middle of the pool x 2)
300 swim (work flip turns)
16 x 25 on :30 (kick underwater in streamline as far as possible)
8 x 50 on 1:05 (25 free/25 non-free)
300 swim (work flip turns)
5 x 100 pull with :15 rest (25 right arm/25 left arm/50 regular)
200 cool-down
Total: 3,400

B (bilateral breathing):
400 warm-up as 75 swim/25 kick on your back
12 x 25 on :45 (descend stroke count 1-4, 5-8, and so on)
6 x 50 with :15 rest (25 breathe to left/25 breathe to right)
300 swim (practice bilateral breathing)
12 x 25 on :45 (kick underwater in streamline as far as possible)
6 x 50 with :15 rest (25 free/25 non-free)
300 swim (practice bilateral breathing)
100 cool-down
Total: 2,300 total

C (other strokes):
300 warm-up as 75 swim/25 non-free
8 x 25 with :15 rest (descend stroke count 1-4, 5-8, and so on)
4 x 50 with :20 rest (25 backstroke/25 breaststroke)
300 swim
8 x 25 with :15 rest (kick with fins)
4 x 50 with :20 rest (25 free/25 non-free)
100 cool-down
Total: 1,500