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How to swim like the pros
Think of a stroke that you would like to improve your technique on.
If you can't decide, then just pick a stroke name out of a hat. The main stroke is the front crawl, but many people struggle with butterfly the most.
Whichever stroke you choose, however good you are at it at the start, learning the perfect technique for that stroke will help you with all of the others. Watch some videos or read some books about that stroke.