IGCSE as pvt candidate

Hello all. Flood me with all there is to know, if am interested in doing some subjects in IGCSE as a private candidate, in India, despite being a part of a school. Do I need any specific permissions from school and inform them of this? How to initiate this process? Who to contact? Please guide. Never done this before. Don't wana mess it up. Any other do's n dont's? I wana ease up my school exam workload by taking some exams privately earlier.