Honestly, as an AGer who has limited swim time, you actually may be better off by just sticking to the real basics, meaning just read/watch basic online youtube swim basics videos, and just ‘swim more, harder.’
I read a bunch of the Maglischo and other swim books, and while the quality is very good, you’ll be wasting your time as a AGer worrying about the finest details that they get into, rather than just swim more, harder.
I only say this because that really is the utmost, cure-all, #1-10 focus of the AGer triathlete. I’m finding you can do literally almost anything you want in the water and improve as an AG swimmer, as long as you’re swimming more, and harder, incrementally.
There’s this myth that AGers are slow because they train terribly in the pool, need coaching to fix their form before they work harder, need to watch more swim-expert videos to model their form, and very little of this is true. **The reason AGers are slow is because they don’t swim enough, and don’t swim hard enough, PERIOD. **
Put it this way - I can swim 1:30/100 for 3000 now no problemo, and if I intentionally do tons of things wrong - drop legs, cross the midline, over-roll, all the stuff beginners do but MORE, I’ll drop at worst to 1:40/100. Def not slower than that. ANd that’s with some really ugly form, like uglier than beginners. The exact same deal will be with the fast swim studs doing 1:10 and below - they’ll drop at MOST 10sec/100 if you tell them to mess up their form, or even mess it up on purpose with weirdo things like chicken arming one arm behind their back.
And furthermore, all of those weirdo swim forms are easily fixed with if you’re up at 15k/wk or more, because you’re developing such a good feel for the water that you’ll be able to move things around as needed.
At this point, I know someone will scream, “well, that’s not true because I see these swimmers at the pool for years swimming all the time and they have ugly form, are slow, and never improve!” To that, I can guarantee zero of these swimmers are swimming 15k/wk+, and are almost certainly NOT swimming hard or even extremely hard for intervals, and likely are the typical non-racing YMCA adult swimmer that is very happy with just doing relaxed laps for an hour. Doing relaxed laps for an hour only gets you faster to a point, and it’s not that fast. Unfortunately, that’s what most adult onset triathletes consider ‘high swim competence.’
Swim more, harder, repeat. Watch some youtube videos, keep those basics in mind as you keep working hard. When you’re swimming as fast as JasoninHalifax, PM him more tips at that point since you’ll have earned it!
I used to do tons of drills, watch tons of vids on technique. Now a have 2x45’ and 1x90’ stupid simple workout while I swim hard (form me). At the moment I do only scull drill and maybe catch up drill during warmup. It’s good way. This is my example threshold workout for ~50 minutes (i’m really limited on time during week days): 
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