Kindly can anyone help mein regarding my preparation of gsa exam. Should i start from biological science and how can i prepare for math section.

Test of Reasoning by Edgar Thorpe for the Reasoning portion
For the Basic Math portion, there is a comprehensive book by JWT on GSA. The Science and Maths portion of this book will be enough for decent preparation.
The General Science portion is dependent on you. Because some people have a Biology background, it becomes easy for them to completely cover the Bio portion. If you analyze the past papers, it becomes clear that long questions from Biological Sciences and Environmental Sciences are given every year. That makes 2 long questions from Section 1. For the remaining two, you have Food Science, Physical Sciences and IT. Among these topics, there always comes shorter questions as part of a long question. As you know, each question comprises of 3 to 4 parts. Therefore, preparing according to the paper's needs will help.
For the longer questions, prepare either Bio or Env.Science comprehensively- choice is yours depending how comfortable you are with both.

Thankyou so much for the guide. It was surely helpful.