depends on your memorizing ability or cramming power.i myself had prepared for Ind o Pak.i took into my account dates of major wars and important issues.the best way to prepare for history is to extricate your own notes after going through two or more good books.this task is to be performed very diligently as what to choose or what to not.but never skip any single important event.i can mention here the expeditions by Mehmud Ghaznavi.They were seventeen in total.so can you memorize all dates?obviously not in my case.so dont bother yourself too much for dates just try to be selective and targeting while preparing any topic of Ind o Pak histroy