So, I'm still working my way through Portfolio Theory and Capital Markets by William Sharpe. It's an excellent book although a bit dry in places. The dryness might be unavoidable though with all the math involved. I highly recommend the book as long as you don't have an aversion to math. As a guest on Bloomberg radio once said, "Math waits for no man". Have a good one and good luck with your trading. Cheers.
Disclaimer: Please only use this information with a grain of salt and at your own risk / for educational purposes. I am not an investment advisor so please seek professional help if that's what you're looking for.