Let me tell you a little secret of the swim world: you do not have to swim 1000m repeats or 5k for time to get faster.
In fact, if you are a beginner swimmer, shorter repeats like 25 to 50m can actually make you faster and more efficient than doing longer distance repeats.
Since swimming fast is largely dependent upon much your body position and pull technique, if either of these two are lacking then you are going to be expending a good deal more energy for very few seconds off your split; sometimes you might actually swim slower.
By swimming shorter and focusing on your form each and every time, you can build your muscle memory with good habits and not have to worry about fatigue breaking down your technique.
Below is a good workout that will build your swim stroke up through drills and then will take that form work and translate that into speed:
5×25 balance drill on 10-15s rest
5×25 side kick drill (go half on your left side and half on your right)
5×25 6/3/6 drill on 10-15s rest
5×25 catch up drill on 10-15s rest
20×25 following this rotation
- Focus on your balance in the water
- Focus on good rotation
- Focus on focus on good hand placement
- Focus on high elbow catch
- Put it all together
Main set 2:
4×50 HARD on 30s rest
Cool down: 2×100 choice of stroke
To do this workout properly, you need some eyes on the pool deck at least initially be it through a video analysis so that you know what you are doing wrong or ideally a coach or friend on the deck who can give you feedback and can give suggestions to tweak your stroke.
This is a great workout to do at the beginning of your season when fitness and endurance is not your primary focus. Then, as your season and your form progresses to such an extent it becomes more of an easy recovery swim rather than a key workout.