GATE

So, let me start off with the basic mantra. Before reading this blog you must make it clear, if GATE is a passion for you. Maybe GATE is not. But, definitely an IIT could change your life. So, it is the first and the most important thing to be focused. Make your goal clear.
If you are damn sure that you want to study in an IIT, don't waste an opportunity to write GATE in your third year. It is a perfect platform to know what exactly you have to prepare. I had many friends who were so keen to crack GATE, but never wrote GATE in third year just for the sake of saving an Rs1000. And, those were the people who suffered heavy losses in the main exam. So, if you are financially stable, do give up a try during your third year itself and do at-least a week's preparation with what all syllabus you have studied till date. This could give you an insight into what exactly the whole system is about.
Correspondence course is a good option. Only Text books are required to cover the full syllabus. But, correspondence material gives you an upper hand. Most of the materials consist of a theory part and an objective part. This could act as a reference and definitely an objective workbook is necessary to guide you. It has got a psychological aspect too. These books could motivate you when you are deviating from the goal.
I followed IES made easy materials. It is good for civil. The theory part of structural materials is unique and even-though they are copy-paste, it make up to the standards. The main reason is that, errors are too less compared to any other. Also it has worked-out solutions to key questions.
ACE Academy books are also good. In-fact, the objective workbook is the best in this case. It covers wide range of questions. But, the main problem is that we will have to solve questions by ourselves.
Elite academy has the maximum number of books and, I personally won't suggest any to buy those books. They are made of some old worn out pages and it kills the essence of learning. Also, there are many errors.
Also, don't rely much on GK Publications book. Some part of the book is really good, like RCS, where, Irrigation etc. But some part are the worst like Concrete Technology.
Coaching: Coaching is actually not needed. If you have the books and proper mindset to study, there is nothing that can stop you. But, if you are a bit lazy, coaching would ensure that you are on the right track and could even act as a revision class for you.