Subtitled The Singular Story of English Spelling, this is a lovely little book which covers its subject very well indeed. David Crystal is a well-known expert on the English language, and it’s good to see him writing something nicely accessible to the general reader.
He starts, sensibly enough with how scholars first tried to represent the sounds of Anglo-Saxon in the Roman alphabet, and moves on through scribes trying to standardise spelling, which is where some of the seeming oddities of our language come from.
Moving forward, you can learn why words light night and fright have that odd letter g lurking in them, and much more. It might not improve your actual spelling, but at least it can give you an understanding of how words came to be formed as they are, and to understand that English isn’t quite as irregular as it sometimes seems. Good stuff, comes with a suitably long index.