If you're a Spotify Premium user, you can listen to Spotify's 13 million tracks from your Android device. Here's how to sync your favorite playlists so you can listen to them offline, without an Internet connection:
Step 1: Launch the Spotify app and click on the Edit offline playlists button.
Step 2: Tap the check box next to the playlist you want to sync. Spotify will immediately begin synchronizing the tracks to your device.
Step 3: When you open the synchronized playlist, you'll now notice a green icon next to each track.
Step 4: To force Spotify to only play music in offline mode, tap More from the menu at the bottom, then tap the check box next to Offline mode.
Step 5: You should now be able to play your synchronized playlist in offline mode.
Offline mode is very useful for listening to your music on planes or in locations that don't have an Internet connection. It's also a good way to reduce data usage by synchronizing your playlists when you have a Wi-Fi connection and listening to them in offline mode.
Note: The number of tracks you can sync is limited to 3,333 tracks, and you'll also be required to log in to your Spotify account once a month to verify that you're still a premium member.