The key for the analytical ability section is practice.

For example when I started Analytical Reasoning practice, a set of 5 questions took me around 15 minutes to solve and even then I got a few wrong. After practising and going through the explanations in the book, slowly I got better at it and now I am able solve a typical set in about 6-7 minutes. The questions in the book get difficult as you progress through it, so if you go through them you should have no problem on the GAT. The things to remember while solving the questions are the rules described in the statements and getting the setup (diagram) right for the questions. Take your time while doing this because this will make the questions very easy. As for the book, do not be scared by the length of explanations offered for the questions, they are there for understanding and for this reason are long.

For Logical Reasoning, I have found the process of elimination to be the best tool. The important point for this section is not assume something which is not stated in the passage (unless it is universally accepted). Again do not be alarmed by the length of the explanations offered in the book. They are there so that we can completely understand the question and explain why other choices are incorrect.

Go through the book as much as you can and if finished look up questions on the internet. I cannot stress enough the importance of practice.

Hope this helps.

Regards