My swim better list goes something like this (these are only a few of the many things that could make anyone's list). Depending on what is going on with life, I try to remember these things and put one of them into play when appropriate:
Swim more often. I know I can get by with two swim workouts a week and still swim OK, but if I want to swim better, I know I have to swim three or four (or five) workouts each week.
Mix up my workout routine. If I am not training for a specific event, race, or meet, I usually go to the swimming pool and do almost the same workout every time. If I want to swim better, I need to mix up my swim workouts; do some of them with higher intensity sets, some with lower intensity; some with longer swims, some with shorter; some pulling and kicking, too.
Do more swim technique drill work. I do some swimming technique work within every workout, but if I want to swim better I know I need to do more. What works for me is to make one of those added workouts almost exclusively a technique workout. I keep doing some technique-oriented sets within every workout, but I make one workout each week a much more technique focused swim.
Get a good swimming catch. I try to swim with an good early vertical forearm or a good catch; fingertips pointed down, pressing back on the water with everything between my fingertips and my elbows, trying to engage my lats and pecs and hollowing my armpit (try a wide-arm lat pull down on dryland and check the way your armpit develops a hole between the lats and pecs). To be a better swimmer, I have to check this arm position very often or I get lazy and let my catch start late or I let me elbow drop or change orientation so I lose some of the forearm press on the water.
Pay better attention to my body position and my hips and shoulders. When I swim freestyle I try to keep my hips and shoulders rolling or rotating, but if I want to swim better I have to check that body roll more frequently, perhaps even doing specific body roll swim drills to help. I tend to get distracted when I am swimming - my mind wanders off to many other places. When that happens, I need to get back in the moment and make sure I have not flattened out, make sure I am still rolling my body appropriately.
Kick more. I tend to let my legs float along, doing an easy, soft two-beat kick. If I want to be a better swimmer, I know I need to kick a bit more, particularly when I leave a wall.
Keep an eyes down head position. I tend to do this pretty well - keep my eyes looking at the bottom of the pool, maintaining a neutral head position so the top of my head points where I am going. Still, to swim better, I need to check this often, as I can sometimes let my head tip up when I rotate for a breath, especially if I am doing an ocean swim.
Make your own list of things you could work on to be a better swimmer. Then use it!