When studying for the Cambridge 'A' Level, I used Economics by John Sloman and Alison Wride. It is a fantastically thorough book, and regardless of which board you're sitting for, you'll find it useful! The book is also great for IB students and undergraduates. It is available online in a PDF (probably got leaked), so you can check it out for free.
Another book I used was Cambridge International AS and A Level Economics by Colin Bamford and Susan Grant. Although this book is geared towards Cambridge students, some topics are explained in great detail, such as the Keynesian theories. This is also available online for free.
Some more tips for self-study would be to use online resources, such as YouTube and Khan Academy. You'll find great videos on Khan Academy about almost anything!
I would recommend more books for you, but it would help if you mentioned which exam you're sitting for! I hope I could help, though.
Best of luck! Cheers.