I used swimming to keep my condition after straining my back badly in competitive weightlifting and thoroughly enjoyed it but it is best to get a professional swim trainer to look at your technique and train with a swim group so that you don’t fall into the pitfalls so many recreational swimmers do. Improving your technique will help not only your effectiveness but is one of the most important things you should do to ensure you don’t get the repetitive strain injuries (particularly around your shoulders) that stop people continuing with this recreational activity.
If you look at the top competitive swimmers you can see how effortless they seem to be able to move through the water and most of this has to do with their efficient technique. Although it takes some effort to improve your technique, it is worth the time and effort to get it right. For those who compete in the multi sports events that have an element of swimming, it is even more important because it usually is the first part to the event and will destroy their chance of a personal best if they haven’t worked at it.
One thing a lot of people don’t think much about is to work on their flexibility and again, if you look at the top competitive swimmers warming up before they compete it should be obvious how flexible they are? This also helps them move more efficiently through the water as well as lessens their chance of injury. Some Yoga routines will help improve flexibility specially for swimming. There are also some basic strength routines you can do both in and out of the water that are specifically designed for swimmers. This is why it will help you immensely if you train for at least part of your time with a swim group under a swim instructor, who will give you plenty of skills training that will improve your strength.
Specifically, people who aren’t effective in their technique in swimming will tend to shorten their stroke length. Their body parts will not be coordinated and will counteract against each other. (You don’t even need to see this but hear it by the amount of splash they make in swimming.) There is a lot of work done under the water in hand placement and how you kick your legs are crucial in swim efficiency. As to whether you breathe on both sides of your body or just one side when doing front crawl stroke is up to the individual, but you get better balance if you can breathe on both sides. Keeping as long as you can in doing front crawl is also important.
I am not going into more specific ideas as I like to keep these posts short, but to reiterate using expert advice is well worth your time if you want to enjoy swimming as a recreational activity.