Double tapping the home button on my iPhone brings up simple audio controlls like prev/next song, play/pause and volume as well as telling me which artist, song and album is playing.
What would make it even better would be the ability to star a song right from the lock screen. Meaning that I don't need to unlock my iPhone (maybe switch apps to Spotify), tap Now playing (because I'm almost certainly somewhere else in Spotify than the current playing playlist), tap the cover art and then finaly tap the star icon. Few! That's an awfull lota work for something so simple.