I am in first year chemical engineering.....so how should i start for gate

It is not a bad idea to start early preparing for the GATE exam. Start familiarising yourself with the syllabus and the past years question papers. So by the time you come  in your final year, you should be all set to take the exam and come out in flying colours.

However, you have to remain consistent during the whole period of preparation, if you are starting early.

I would also suggest that you go through the link that is given below as it will guide you in your preparation.

How to prepare for GATE - chemical engineering