I regularly find that I'll understand where the field content in a particular physics paper comes from, but then a Lagrangian or action or superpotential is stated and I don't know how it's derived. Is there a set of general rules for building a Lagrangian/action/superpotential if you already know the field content of the theory?
Any suggestions of sources that explain how to do so would be very welcome as I'm having little trouble finding much that helps.