There are just a handful of tenets you need to subscribe to in order to improve your swim. Swimming well is enormously dependent on technique. Survival swimming is a different story. You've already realized that survival swimming is not the greatest way to get through a triathlon or open water swimming competition. So what do you do next?
You can watch lots of videos on Youtube. There are a number of pretty good explanatory drill videos and even a handful of longer discussions.
You can join a local US Masters Swimming team. These teams usually have all level of abilities, and coaches on deck to run the workout and provide you with technique feedback. A lot of newer swimmers are intimidated by these groups. You have nothing to fear. Every person in the group was once someone who did not know the difference between early vertical forearm and Splashy McSplashyface.
You can have a couple individual lessons with a technique coach. This is a good investment of time and energy to quickly identify the key issues you need to work on.
You also need to get in the water! Without practice, you'll just be a video watching- and article reading expert. When you do get to the pool, your practice needs to reflect your level of ability.
Swimmers at the beginner level may swim 2-3 times per week. Pure competitive swimmers train more in the range of 5-9 times per week. Most adults are not professional swimmers who can get to the pool every day, and sometimes twice a day. So, you need to figure out how much time you can devote to your swim, in tandem with whatever other goals you may have like triathlon training, strength training, and so on.
I usually recommend 3 swim sessions per week to maintain the balance of time and life demands. Athletes competing in long distance marathon swims or with high-achieving goals in US Masters meets should swim more often.
Beginners: You should focus the bulk of your practice on improving technique with swimming drills. There are a bunch of drills out there, but for beginners you need to focus on the essential basics. Body position, comfortable breathing, and forward reach/extension. A practice like this can and should consist of lots of 50 yard repetitions of drills, a few 50s of kicking (fins if necessary), and just a bit of steady endurance swimming towards the end of the session. Essentially your drills training to endurance swimming ratio should tilt towards 75% / 25%.
Intermediates: As your mastery of the basics improves, you can graduate to more advanced drills. You should also start spending a larger percentage of your practice on improving strength and endurance. As an intermediate swimmer, your practice should be about 30% technique specific focus, and 70% 'just swimming'. That is a qualified 'just swimming' as you should continue to swim with good technique during these warm ups and main sets.
Advanced: Once you've conquered the key techniques involved with swimming, you can spend less time actively doing drills, and more time training speed, strength, and endurance. The key here is that advanced swimmers have ingrained patterns that continually reinforce good technique habits. An advanced swimmer should have a level of awareness of technique at all times during a workout. The ratio here for drills to training is closer to 10% / 90%.
All swimmers should break workouts into separate sets. I know some newer swimmers like to jump in and just swim laps. This is exercise and technically is training, but it is training without purpose. An occasional steady endurance swim is appropriate when training for longer swim races, but should be in the 1 time per 2-3 weeks when approaching your key event.
Workout structure for beginners
Warm up 200-300 yards, break as need be
Drills 8-12 x 50s working on specific technique issues
Kick 2-4 x 50s
Main set: swim 4-8 x 100s steady
Workout structure for intermediates
Warm up 300-500 yards, mix it up with optional non-free stroke, break as need be
Drills 6-8 x 50s for specific technique issues
Kick 4-6 x 50s or mix within the main set
Main sets: Between 800 to 1,500 yards with various effort levels
Cool down: 50-100 easy
Workout structure for advanced
Warm up 500-800 yards, mix it up as above
Drill/kick mix 8 x 50 or so
Main sets: 1,500-2,500 yards with various effort levels, can include sprints, equipment, hard kicking, and so on
Cool down: 100-200 easy
In general, main sets are broken up swims: 100s to 500s for endurance, 50s to 200s for mod-hard/tempo efforts, and 25s and 50s for sprints.
You can read more about swim training on the general internet, and we have a few articles archived on the One Step Beyond article page.