How do I mix music from GooglePlay and ITunes?

If you're using Windows, simply add the download directories for both Google Play and iTunes into your music library by doing the following steps in Windows Media Player:

- Right-click on Music in the left-hand pane -> Manage Music Library

- Click "Add" and select the download folder you want - for iTunes this is normally [user folder]/Music/iTunes/, for Google Play it can vary

- Click OK and the folders will automatically be imported into Windows Media Player which will update automatically whenever you download new songs from either service into the watched folders

You can alternatively use Google Music Manager to automatically upload just the iTunes folder and listen to all of your music online through Google Play, or use import your Google Play songs into the iTunes desktop application. I don't recommend doing the latter as iTunes is stupid and doesn't automatically scan for new music, so every time you want to add music that isn't downloaded from iTunes you have to manually add it to the library (both of these other solutions also work on Macs as well)