Reddit mentions of Simple & Direct

Try out cleanth brook's book on writing and rhetoric. Also Jaques' Barzun's Simple and Direct. I assume your problem is expressing yourself clearly and effectively. Since you are a grad student, had you had problems with basic logic you would not have arrived where you are already.

EDIT: On the level of organizing thinking, these books will also help:

1. George Polya, How to Solve it Although it is about mathematics, I would recommend this book to anyone studying in university. It's a book about "thinking outside the box" if understood properly.
   
2. David Hackett Fischer, Historian's Fallacies. Studying the types of mistakes in informal reasoning is always instructive. This book is a good study of such errors in the field of history. I would also suggest checking out the various lists of argumentative/logical fallacies that can be found on the internet (I recommend the book because it is good).

https://www.amazon.com/Simple-Direct-Jacques-Barzun/dp/0060937238