It requires an outsider's eye. Given the highly competitive nature of the market place, wasting a valuable contact with a producer or publisher by having them consider less than accomplished material is foolish. Although proof reading is important, it is only the minimum level at which a piece should be reviewed. A critique includes checking continuity, consistency of style, and plausibility along with all of the many factors that can make your product literature and an enduring work of art. I can provide more thorough service if a client involves me early in the process.
Clients are wise to seek professional services when they are formulating the concept for their work.
Collaboration often shortens the road to success. If you have an existing work in one of these forms, I can transform it for you into one of the others. If you have an idea for a work, I can help you determine which form is best suited to bringing out and realize your vision. As the client it is presumably your own work that I would be adapting. You own the rights and would be commissioning the adaptation.