Creators of popular mixing & mastering plug-ins such as Ozone, Alloy, Nectar & Insight, iZotope, have recently released a number of guides related to mixing and mastering. Both of the guides provide a great amount of insight and cover a wide range of topics in depth. They are perfect for both beginners and more advanced audio professionals.
Both of the guides clock in at over 50 pages and contain not only tips form iZotope themselves, but also a number of industry professionals.
We thoroughly recommend that you check them out, you can find them here.