I recently read two books focused on website performance.

Designing for performance (weighing aesthetics and speed) by Lara Callender Hogan.

Responsible Responsive Design by Scott Jehl.

The first book is interesting and a very good primer for new developers or for folks that have never considered web performance based on design trade-offs. The second book was a very handy manual of sorts and was my favorite.

I would reccomend reading both if you haven’t had a chance. They should be available from your local library through inter-library loans.