Training sets and fitness goals are a great way to improve your current swimming ability. More often than not, I see people swimming lap after lap, stopping, then doing more. However, you will probably get pretty tired and bored doing the same work over and over! Also, swimming just one stroke focuses on certain muscle groups rather than your entire body.
I believe that it is important to have a mix of strokes and sets which focus on a variety of heart rate zones to cover all your bases. By doing this you, will be able to build up stamina and speed, as well as technique across all four strokes.
To find out more on the technique of all four strokes check out the article on the strokes here.
By developing a training session that has a mix of all four strokes, not only are you able to mix up the sessions so you don’t get bored doing the same session every time you are in the pool, but you are also targeting all the different muscle groups that you use when you swim the four different styles.
Try implementing set programmes on a set time. This will help you to make sure that you are getting to the right heart rate zone. An example would be a set like 12×100 on 1:40, holding the best average speed you can hold. Compared to implementing a sprint set that involves 12×25 on 1:30 all dive sprints focusing on the quality of the sprints rather than the distance.
By having diversity in your training programme you will get more out of your sessions each time you get in the water, you will enjoy your sessions more, and you will more likely than not improve at a faster rate due to all of the above mentioned factors.