I've done stuff before and had a tendency to want to add instruments to create interest really in fact (probably without realising ) to compensate for some pre existing inadequacy . It's important I think to go back to the core of the song and ask yourself if it's really working as it should with say a guitar and vocal on its own . Melodically, dynamically ,in clarity of recording technique , lyrically every possible way. The chances are there's 10 times more to improve there than moving on at all. That's really what I'm consciously learning from past failures