In no particular order, I thought I'd gather some things I learned so I don't forget them and to hopefully help others.
1. Goggles fogging up? Spit on them!
At the advice of the good people on the RunningRoom.com forums, I spit on the inside and rubbed it around a little... as gross as it sounds, this actually worked. No fog. Fantastic and free!
2. Get a tri-specific wetsuit
I bought a cheap Ski-doo suit at Costco... seems it's ok for practice but it's not nearly as good as a true triathlon suit. Might be great for jet-skis!
3. Drink water while you swim
You're surrounded by water, but none of it is getting to your stomach (hopefully!), and even though you don't notice it, you sweat when you swim. So replenish the water as if you were on land.
4. Look straight down, not forward
The tendency is to look forward as you go along, but looking straight down helps bring your feet up.
5. Bring your feet up!!!
My feet drag below the surface. I don't know how to fix this yet... something I need to work on. But when I put a flutter board between my knees to keep them up, I was so incredibly fast, instantly! So I know this is a key to efficient swimming... I'll post here when/if I figure out how to solve this.
6. Don't reach straight out, reach down
I used to reach out as far as I could, then push down on the water at the start of my stroke. What a waste of energy! So now I plunge my hand forward under water at an angle, about 45 degrees to the water surface... and all the arm strength goes to propelling me forward, not up.
7. Breathe with the diaphragm
Taking a deep breath from my stomach helped me keep my breath longer. But if you're like me and you find yourself gasping for air, it's probably because you're horribly inefficient and need to work on technique. I sure do!
8. Breathe out under water, breath in above water
It's important that you exhale under water, not above... don't hold that breath!
9. Don't kick like you run
My kick needs a lot of help, but the first order of business was pointing the toes. This may require some stretching to be more ballerina-like. If you run, you probably point them, but the wrong way! I read that some people end up going backwards when they kick because of this.
10. Swim fresh
When you're learning technique, it's best to take a lot of break to keep your breath, rather than trying to push through your panting. When you're tired and out of breath, your technique is going to be terrible. Swim slow and smooth rather than trying to go fast when you're just learning, and keep your breath. Endurance will come with practice (I'm told!).
Hope that helps. :)
I went from not even being able to exhale smoothly under water to being able to do some nice laps in a few months of practice and lessons. I have a long way to go, but I've come a long way, and there's small improvements and discoveries every time I get in the pool.