1) Do the homework on company, the product it sells, the presence of company in the othe business. 2) Get to know what are the things u will have to do if u join the company, I will suggest to talk to ur senior who are working there. 3) In my case they have asked me some basic questions like, a) what is CNG and LPG, how both are different, what are the properties of each. b) types of defect in welding, welding inspection tests. c) difference in pump & compressors, different types of compressors and pumps. And at last I will suggest u to prepare ur resume, let ur friend ask questions from it, prepare ur strength and weakness & align ur weakness such that it doesn't harm ur working.