As a seasoned fish keeper myself when first coming here with over double your years, I learned something which was the most important part of fish keeping and my life has been much better for it since. That is about Beneficial Bacteria aka BB and about how the nitrification cycle works. That was the best most useful piece of the puzzle.
But the most key point was not changing your filter pads until they fall apart (and I will add an additional pad -2 instead of just one for even more surface area for bb). And to not wash it off in tap water that has BB killing Chlorine and Chloramines, etc.
Also using Prime as a water conditioner and safety measure in an emergency.
I guess that is actually more than one thing but all some of the most important things.
Don't over feed, and keep water quality good and frequent and appropriate amount pwc
The thing about Ich is it opportunistic. Stress, new fish, more feeding due to fry, not having enough BB to process water adequately (poor water quality). Always temperature match the water and err on the side of a degree warmer rather than cooler.
These things should help with care of tanks which will make the learning about new fish more fun, because when you get them, you will be better prepared for keeping them happy and well.
Learning about new fish, consider their size as adults and what conditions they prefer as well as if they are loners or prefer a shoal of buddies, etc. Selecting the right combination of tank inhabitants will provide a more contented life for you and the fish.
This is an awesome fun thread about Cories for you to look through