1. Stop kicking so much
What works on dry land most definitely does not work in the water. Our leg muscles (especially the quads and the hamstrings) that have been so wonderful at propelling us land-based bipeds around for a million years or so are not very effective at moving us through the water when doing front crawl.
We only need to get about 10-15% of our forward momentum from the leg kick when doing front crawl for endurance training. So, keep the knees straight, point the toes, kick from the hips, and relax. Hang on, let me say that again, a little more emphatically...
2. Relax. Stop fighting the water
You WILL lose that fight. It has been here a lot longer than you have, and covers much more of our planet's surface than you will ever see in your lifetime. When was the last time you saw a tense dolphin?
That's right, dolphins are mammals, like us, and they have learned how to handle the water. Relax, undulate, glide, straighten out, and work with the water, not against it. Seriously, once you relax and trust in good swimming technique, you will relax, your breathing will improve, your body position will improve, you will start listening, feeling, and moving with greater sensitivity and effectiveness.
3. Ignore the advice to stop kicking altogether
I know it sounds like I am contradicting what I said above, but I'm not. You need a small, streamlined, gentle, consistent kick, mostly for stability and streamlining to create less drag with the legs.
The muscular engagement mentioned above (kicking from the hips) will also help engage the glutes, the lower back, the lower abs and those all-important core muscles, keeping your spine straighter and travelling all the way up your body for more overall improvements. As you work on intermediate swimming technique, like effective upper-body rotation, you will be glad that you developed a gentle but steady kick that gets you using the core more effectively.
4. Little and often is usually best
I know that swimming is perhaps the hardest discipline to work into our daily routines, as it is something that we can't do as a commute to work or any old time or place we feel like it.
But, it really is better to swim three times a week for 30 minutes each session than it is to swim once a week for 90 minutes in a mammoth single session. Three times a week or more will allow your body and brain to remember the technical focus that you worked on previously, whereas if you swim once a week your body will probably forget most of what it did last time.
5. Don't just bang out loads of distance, swimming length after length after length without any attention to technique
Technical drills make an excellent way to warm up and cool down, and doing them at the beginning and end of every session helps ensure that you remember what makes for good swimming: good technique.
Will you ever get to the point where you are so good, so naturally gifted, that you can stop practicing swimming technique and technical drills? No. You know someone who is a really good swimmer? I bet they do technical drills a lot, maybe even every time they go swimming. If they don't, then they probably aren't as good as you give them credit for.
6. Start off really gently, so much more gently than you think you should
In swimming sessions, in group sessions, in private lessons, and especially in races, I see triathletes always starting off way too fast and way too intense, then they get really really tired, gasp around for air, struggle a little bit, and then get forced to re-set their internal pace clock to a much lower setting and carry on from there as best they can.
One of the single best things you can do with your swimming is to slow down and take it easy from the start. Save some energy for later, when you might really need it.
7. You can't teach yourself to swim
You really do need to get some objective feedback and instruction. Reading books, watching videos, and following instructions are all helpful, but ultimately you will need to get some professional, experienced, coaching with your swimming.
Video feedback also helps TREMENDOUSLY. Seriously, it will blow your mind every time you see yourself on video when you are swimming, and it will definitely accelerate your learning process immensely.
8. We are, by definition, endurance athletes, unlike most ordinary swimmers
We call an event with a 400m swim a "super-sprint" and a 750m swim a "sprint". Ordinary swimmers would tell you that's crazy, that's more like middle-to-long distance swimming.
So, we will need to learn how to swim very differently from people who are training for 25m, 50m and 100m events, and we need coaches or swimming instructors who implicitly understand this and teach a style and approach that works best for us, as triathletes.
9. We need to be able to jump out of the water, get changed, get on our bikes and ride, then get off the bikes and run
This means that we need to be able to finish the swim feeling strong and healthy enough to finish the remainder of a gruelling event, rather than feeling like we gave 110% in the pool (or the lake or the river or the ocean...).
We need to be efficient, we all want to be fast, but maybe only using 80-90% of our maximum capacity. This is also why swimming technique is so vital to triathletes, so that we are not wasting a lot of energy overcoming drag and bad swimming technique, but swimming smoothly and effectively through our events.
10. Learn how to swim straight
Probably the best thing you can do to get faster and more efficient at swimming in open water is to make sure that when you enter a 1500m race (for example), you swim as close to 1500m as possible, and not more like 1800m.
This is a huge topic, which could probably use a whole article all on its own, but I will close this for now with a few final pointers on the subject. Some people will try to simplify things and tell you that the best way to swim straight in open water is to sight more often (which involved looking up and ahead of you to see where you are going), and this is really not the best advice.
Good swimming technique is really the best advice, especially when good swimming technique means having a balanced stroke with a straight body position, a balanced kick, nicely balanced upper-body rotation, straight hand entry, pulling through a straight line under water, and generally doing things correctly in your swimming technique.
After that, there are loads of open-water-specific things that you can do better, too.
Rob Popper is a Level 3 Triathlon Coach and director of Triathlon House, with an endless pool and video analysis system in W2 3RG. He has been a triathlete for 12 years, and he actually got started on the path to becoming a triathlon coach when he had an endless pool video analysis session with Swim for Tri about 9 years ago. He was so blown away by their coaching skills that he wanted to become a coach, too. He is eternally grateful to Dan Bullock, Keeley Bullock, Ray Gibbs, and Dawn Hunter for helping him to fall in love with swimming, swim coaching, and triathlon coaching, as well as showing him the Way.