I posted this on the DecaDynasty hints, but it's also useful for people trying to do an Immortal Dynasty Challenge.
If you have University Life, and are trying to supermax the writing skill, I highly recommend doing Sports Books. They're short (around 125-130) pages, and can yield 600-1500 simoleons. By the time my sim had written 20 books (the second skill challenge), he had also received 30,000 in royalties and of course completed the 3rd challenge.