One of the neatest features of stock Android is the lockscreen controls that appear while you're listening to music. What you might not have known is that you can long-press them to jump to a specific part of a song.
The lockscreen controls were introduced in Android KitKat, but the long-press functionality has flown somewhat under the radar. Simply long-press on the title of the track, and a slider will appear that lets you scrub along the song. Easy peasy!