Outsider art and primitive art share a common trait, they are made with limited resources. These limits may be raw materials, knowledge, or adverse conditions. In spite of these obstacles, these works of art have a spontaneous energy and immediate appeal. The intellectual lurks inside the emotional.
As artists we strive to improve. We practice our craft. We critique and develop our pieces. But skill is not enough. There needs to be an element of the unknown, the leap of faith where art transcends the artist. Creative people try many ways to get to this liminal state where creativity thrives; isolation, meditation, exploring nature, drugs and alcohol. To some degree, they all work, but each has it's drawbacks.
Now consider the limitations of primitive art, the artist must create despite the lack of some element. You can do this in your own work, just try to make something without your regular tools. For a musician, try to play or write a song on an instrument you don't know. For an artist, try using some inappropriate medium. For a writer try limiting your vocabulary in some way.
Lately, I have been using a pocket-size drum machine and a 4/6 channel mini-mixer. I can put guitar, bass and vocals through the mixer and recording on a guitar looper pedal. This means I can overdub but I can't edit tracks... Once it's on there, it's there for good. I end up making endless versions of the song which causes me to rethink almost everything. The end results sound primitive but listenable. When I get into a real studio with these tunes, I will have a good idea what to do.