PA written
By rights, you should approach your Private ground school as an academic exercise. You should concentrate more on learning the knowledge because you will need it as a pilot. The written will take care of itself.
Having said that, get the ASA book. The ASA book is the test. Go through all the questions and see how many you answer correctly. That will be a good gauge of your knowledge. Then, you can go over and over the book and essentially memorize the questions and answers.
Finally, looking at it in the long term, after you take the Private written, go back and take the Basic Ground Instructor written. The exam is exactly the same as the Private written, but just more questions. Later on, take the FOI written, turn in both written test reports to FSDO, and leave with your Basic Ground Instructor certificate. Later, you can take the Instrument Ground Instructor written when you take your instrument and FII writtens and upgrade to Advanced and Instrument Ground Instructor. The point of all this is you get another credential to put on your resume, which is always nice.
Good luck with the written. As you can see, this is the first of many.