You want to prepare for GATE. You can appear for GATE from 3rd year of engineering. So firstly you should have a brief knowledge of all the main subjects in your engineering syllabus like microprocessor,basic electronics, Electronics Circuit,Network theory,Computer networks ,Control Systems and others. For this subjects you can get a standards good books list at Made Easy Site (http://www.iesmadeeasy.org/IES-booklist.asp).After a brief knowledge in these subjects you can take GATE guide to check out your practice on these subjects for GATE. These days many GATE guides are available for GATE but the best GUIDE is delivered from MADE EASY Publication. If you need any more help ask me.