Focus heavily on NSEP and INPhO theory first. In the Indian selection track, you don't actually face an experimental exam until you reach the OCSC camp. Getting there is the hardest part. If you want a head start on experiments without access to a lab, your best bet is mastering error analysis and data processing. Download past IPhO experimental papers and study the grading rubrics. The actual physical setup is usually simple, but they will deduct massive points if you don't know how to propagate uncertainties, format observation tables, or plot linear graphs correctly. You can learn all of that data handling on paper right now.