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You should know IES syllabus and compare with your college syllabus. Topics which are matching, try to cover it by class and NPTEL lectures which you can easily access at youtube. For the topics which will be uncovered in lectures watch it from NPTEL lectures.
The most important thing in preparation of IES is the selection of books. My advice will be always going for standard books, not local author's book. If you can then try to have notes of IES preparing coaching as Made easy notes. Which you can get from photocopy shops beside made easy Delhi.
Developing conventional approach is a must for IES. For prelims your vast knowledge matters and objective approach too.
If you can afford then join any available and suitable coaching for this according to your ease. But, it should be done after having rock solid basics.