The best way to learn how to mix, is to mix more. Before you can do all that, though, you’ll need something to mix. If you’re not at the stage where you’re getting clients yet, or you don’t have time to record a huge amount of music yourself, multitracks are a great option. There are plenty of multitrack recordings out there that you can download for free and start experimenting with.
I’ve pulled together three free resources to make things easier.