GATE

Hello Ravula,
GATE 2019 will be conducted by IIT Chennai and they have displayed a very nice webpage where all the required information is available. You can download the syllabus for all the papers that you are interested in preparing for so that you know how and what to study. However for obtaining old question papers along with answers you will just need to Google and you will find hundreds of web pages with this information. As a counsellor of Shiksha I cannot recommend a particular agency or particular institution as it is against the policies hence I would advise you to make use of Google and download all the information that you want and which is easily available on the net. http://gate.iitm.ac.in/Syllabus
Best wishes to you for your GATE 2019.

It is very good that you start your preparation right from the first year of college. Two years of rigorous study have paid off, and you very well deserve a break. Studies include basics of every branch. Just observe everything, and make sure you want to get into technical side, i.e GATE / ESE. Second year usually has some important subjects, make sure you don't study them just for clearing the semesters, but for getting in depth knowledge. It is very tough to do that, but once you do that, it will pay you off very well 2 years later. In the 3rd year, join a coaching. Or, arrange some good study material and start serious preparations. You won't get that much time in final year, plus a head start is always better. In the final year, revise and repeat. Infinite times. Join a few good test series. Attempt all tests. You will gain the momentum that will surely help you perform well on the day.

Power electronics - P. S. Bhimhra
Power system - Nagrath kothari
Electrical machines - P. S. Bhimra
Networks - Valkenburg (Madeeasy notes are sufficient)
Control system - Madeeasy notes (B. S. make, nagrath kothari)
Analog - Bolyested
Signal and system - Madeeasy notes
Op-amp, filters etc. - D. Roy Chaudary
Digital - Anand Kumar
EMT - saiduku
Measurement -madeeasy notes
Engineering mathematics - Ace academy and Madeeasy notes (I followed H. C. Taneja for some part). For questions - Madeeasy book containing previous year questions and R. K. Kanodia
Apart from these I will recommend you to follow Madeeasy handwritten notes. They are extremely helpful and will help you in identifying portion related to syllabus. NPTEL videos are another best source for getting your doubt clear if you are preparing your own. Best of luck!

You have two option before you start, either to prepare your own or take coaching. Now according to me first one is the best. Coaching will be helpful only when your basic are not at all clear. First download the syllabus and then start preparing. You can refer to the following books:
Power electronics - P. S. Bhimhra
Power system - Nagrath kothari
Electrical machines - P. S. Bhimra
Networks - Valkenburg (Madeeasy notes are sufficient)
Control system - Madeeasy notes (B. S. make, nagrath kothari)
Analog - Bolyested
Signal and system - Madeeasy notes
Op-amp, filters etc. - D. Roy Chaudary
Digital - Anand Kumar
EMT - saiduku
Measurement -madeeasy notes
Engineering mathematics - Ace academy and Madeeasy notes (I followed H. C. Taneja for some part). For questions - Madeeasy book containing previous year questions and R. K. Kanodia
Apart from these I will recommend you to follow Madeeasy handwritten notes. They are extremely helpful and will help you in identifying portion related to syllabus. NPTEL videos are another best source for getting your doubt clear if you are preparing your own. Best of luck!