hi,

its not clear in your questions which exam you want to study for. however I assume it is gate exam, most of the students opt for gate exam who want to pursue mtech or want to do job in psus.

the proper time to start the preparation is 3rd year or from 4th semester, since at this years you have got all your core domain subjects.

there is many coaching institute is available, but you need to mostly focused on self study, because unless you give your hundred percent, you can not expect good rank by studying on coaching center notes.