If you're talking about writing a thesis from scratch, Umberto Eco's How to Write a Thesis is a great starting point. It's a step-by-step guide for conducting background research, formulating research question and structuring and writing the thesis.
As long as you pass the threshold I don't think GRE really matters for professional program.
I have lots of friends with lower GRE scores now attending SIPA's MIA program (some of them even have funding!)
One of the assistant deans of SIPA said that what really matters to them is a candidate's overall profile, especially his/her experience, and that GRE is more like an admin procedure and a very rough screening tool.