You gotta do more than just swim as far as you can.
You can break it up in different sets, there are endless amounts of sets you can do.
Depending on the level your at I would recommend starting off with an easy warm up maybe 5/10 mins steady swimming.
You have do do some drills in order to get better. Just simply swimming will not be of any benefit, the more you swim with bad technique the worse you will get. Especially if you swim til exhaustion each time. Technique gets worse as you get tired.
Have a look on Youtube for freestyle drills or backstroke drills. Work on these and then move onto breaststroke and butterfly at the end. So after a loose warm up and another 5/10 mins of drills I recommend you go into a set.
One thing I see loads is people going in and just swimming. You can do kick which is very beneficial for your legs and kick technique. Without your kick, your hips will drop and your arms have to work so much harder. SO learn to keep kicking during your swimming to keep hips up. This will improve your stroke and make you faster.
So you can think of your own sets but ill give you a few examples.
4x25 Fast Frontcrawl kick with a float (Rest 20s)
4x75 Frontcrawl Swim at a steady pace (Rest 15s)
4x25 Fast Frontcrawl Kick with a float (Rest 20s)
4x50 Frontcrawl swim fast (Rest 20s)
You could go through this twice for a set of 1400m. Combined with drills and warm up you could be getting close to 2000m. Do this a few times a week and you would see great improvements.
Or another more aerobic set could look something like-
1x200 (Rest 15s)
1x150 (Rest 10s)
1x100 (Rest 10s)
1x50 (Rest 10s)
Starting with the 200 at a steady pace and descending down until the 50m is fast. Do this twice for 1000m.
This could get you started, but there are so many things you can do. But I would not go in and simply swim. You will get bored very quickly and just stop swimming. You have to keep it new and exciting.
Maybe do a 100m fast at the start then after a month or two months do the 100 fast again and see your improvements.
Hope this helps.
