Very readable book that covers the basics well:
Tactics for Trout, by Dave Hughes
Sightly more advanced, for some of the finer points of the art:
Common Sense Fly Fishing, by Eric Stroup
I found both of these very easy to understand. Nothing beats getting out on the water, but you'll have some idea where to start if you read Hughes book. And you'll have more of an idea how to solve some of the problems you have to solve if you read Stroup's book.
There are other books, some just as good. These two have the advantage of putting a lot of info into a few pages.
After that, there are a million others that look at some more specific aspect or another.
I'd study your knots, too, and practice tying them. You get get guides to that on-line.
For a fact, there's a huge amount of great information on specific situations, problems, and challenges right here in this forum. You can check up on that just by doing a search. But for best results, you need to get out there and fish first, so you'll know what questions you want answered.