Dear sir,

my name is chandramouli. presently iam doing my b.tech 3rd year in mechanical engineering , i want to prepare of gate exam. please give me some instructions to how to prepare for gate,

Preparation time for GATE is subjective and depends on many factors such as individual's aptitude, fundamentals, attitude, concentration level etc., Typically, a rigorous preparation of 4-6 months is considered good enough.
Start reading all the chapters and prepare short notes on all important points. In this way, your revision is also complete. These short notes will also be useful for your last-minute revision. Solve objective type (especially numerical) questions as much as possible.
Go through previous year papers (say last ten years), to check your knowledge and note the distribution of different topics
good luck!