I concur with everyone here. Exam Krackers seriously is the book.
However, if you are pressed for time I would suggest reviewing the Kaplan book (very) thoroughly. Then take Top Score and use your mistakes to recover those topics that you had weaknesses in.
There are several reasons why you might want to do this. Reviewing the Kaplan book first lets yo have an idea of the material that is specific for the DAT. You'll find that the DAT requires you to only cover some basic organic reactions and topics. In other words the Kaplan book is to the point.
If after using it, you find that you want some improvement (BTW getting anything above 20 on Top Score will very likely get you a solid scores in the middle 20s in the actual DAT), you can review those topics again or start anwsering questions in Exam Krackers on those topics. The technique with that is do the questions in groups of 50 and mark your answers right or wrong, then go back to wrong answers and try to select the right answers from the remaining choices without looking at the explanations. Keep doing this until you get them all right. Then review the explanations for everything you didn't get right the first time or anything you were doubtful on but got the correct answer somehow.
I firmly believe in the thorough review, followed by diagnostic test, followed by directed study technique. This way you can concentrate on nomenclature or free radical addition or whatever area you feel you need to improve.
As for methods of learning, I agree with everyone who said that you must understand mechanisms with an emphasis on the word "understand." DAT questions will make sure that you can run through a reaction in your mind (of course you're free to use the scratch paper during the test). This is an essential skill to ace the DAT organic section.
Another thing I would say is to take the actual test as soon as you are ready, if you wait you will likely forget things. It doesn't hurt to take the test early as you will do well if you are prepared judging by your Top Score Pro scores. This also allows you to retake the test in case you really need to (which you won't need to do if you go in getting good scores on the practice tests).
