I just wanted to add, I have finally gotten writers block. (req for Bestselling Author aspiration)
After maxing writing, sitting at the desk from morning to night .... everything I could think of I was starting to give up and think about cheat options. As a last ditch attempt I made a 3x3 room. Put in the worst desk and worst chair I could find. No paint on the walls, no covering on the floor, her nice computer (so it wouldn't break) and that is it. Maxed all her needs, and sent her in to practice writing and removed the door.
Writers block or die in there girl !
13 hours later ....... win.
I am not sure if there is an easier way to get this, but if you are desperate and have a spare day in your sims life, I think this is a guarantee. Mb someone else can give it a go to confirm. It might be easier if your sim hasn't already maxed writing. I am not sure.