Nice site I can highly recommend if you need to improve your skills with mixing multi-tracks​

The 'Mixing Secrets' Free Multitrack Download Library
Below is a list of raw multitrack projects which can be freely downloaded for mixing practice purposes. All these files are presented as ZIP archives containing uncompressed WAV files (24-bit or 16-bit resolution and 44.1kHz sample rate), without any effects or processing. When importing them, just make sure all the track files start at exactly the same moment in time within your DAW project. (Download problems?) In addition to theFull Multitrack packages, there are also many quick-download Edited Excerpt versions (usually featuring the song's biggest chorus) which provide 'bite-sized' mixing assignments well-suited to classroom use. In both cases a preview mix is provided for easy auditioning while browsing through the list.

As well as the multitracks hosted directly on this site, I've also included links to a few other decent downloads I've discovered on other sites. If you have any projects of your own that you'd be willing to post (or link to) here, then do get in touch. This is a continuously expanding resource, so if you want to keep track of the latest uploads please subscribe to my monthly spam-free 'Small-studio Secrets News' mailing list -- I usually post towards the end of the month. Many thanks to the artists and engineers who have kindly agreed to provide these files -- please follow the links and check out their latest music!

Link: http://www.cambridge-mt.com/ms-mtk.htm