Based on experience of some of my friends who have secured top ranks in GATE here are some tips:-
1> Firstly you need to be thorough with the basic concepts of all the subjects of your respective branch.
2>Always try to make notes in your own language,so that you can recall them quickly.
3>Always make brief and point wise notes avoid copying the paragraphs from books.
4>Use a Standard book which covers all the basic concepts avoid using less known books as they may contain some wrong information.
5>Buy a good book which contain previous solved papers.
When you are finished with basic concepts try solving previous papers.
6>If you are unable to solve them take help of the solved papers.If still u cant solve them take help of your professors or teachers discuss them with your friends.
7>Make some practice of general aptitude questions as they are really a great advantage u can score in this section easily.
8>At last try solving the model papers and mock test papers you will get them on internet or you may join any test series like brilliants.
The last but not the least make a group of friends preparing for GATE and discuss your problems and queries with them.
Selection in GATE is not a cake walk, work hard and manage your time well you will definitely get success.