I've always recommended covering a favorite song or two to beginners as an incredibly informative way of learning how songs are constructed and arranged. But even for experienced song writers, analyzing how another artist's songs are constructed can be incredibly illuminating. Especially if you try covering something outside the genre you normally work in. Do you make electronic dance music? Try covering a rock song. Or vice versa. Find something outside your comfort zone and try to reproduce it as closely as you can. You'll learn an amazing amount and it'll broaden your musical vocabulary immensely.
Many musicians are quick to "poo-poo" genres they don't like or listen to in their spare time, but this is a huge mistake. You can learn something from every genre if you allow yourself to, and even if the practical application in your own music isn't immediately obvious, you'll soon realize you have a lot more directions to experiment with that you might have before, and ultimately, that's what helps artists develop their own unique style. Maybe that intricate prog rock drum fill you learned to program would sound killer in an industrial song. Maybe producing a hip-hop song using the sounds and production techniques of drum n' bass would yield something interesting. Maybe that jazz chord you learned would help give a bit of spice to that guitar riff you're working on (it worked for the Police's Andy Summers).
The important thing is you are almost guaranteed to learn something, and at the end of the day, that's what growing as a musician is all about.