Book Review: The Ideas Behind the Chess Openings - Reuben Fine
This, like "How to beat your dad at chess", was recommended to me by a member of my chess club. The idea behind the "The Idea behind the Chess Openings" is to inform the reader of the principles underpinning various openings, rather than trotting out rote lines. The benefits of this approach are that a) it is actually pretty difficult to memorise many variations and b) there is always going to come a point in a game when you are "out of book", so you need to understand what the moves you are playing actually do.
The main downside of the book is that it is slightly out of date. However, if you're playing at a lower level like me you probably don't need to know about the very latest advances in theory.
I've found it pretty useful in understanding queen pawn openings in particular, which I frequently face OTB, but rarely get practice at online. The book is logically organised into chapters on King's Pawn openings, Queen's Pawn openings and so on, then into sections within these. Here's a bit from the book.
"The basic ideas in the d-pawn openings are, in a manner of speaking, a mirror of those in the e pawn section. Here after d4 White's goal is to get his pawn e4, just as it was d4, after 1.e4. Essentially the idea is the same in both: to set up pawns at d4 and e4. " [from the general introduction to d pawn openings]
As you can see, whilst it covers general ideas in each section it does also go into actual lines as well. You can pick this up cheap second-hand like I did online. It's probably more than enough opening theory for someone at my level.