I recommend you to start preparing for General Paper right from the beginning of your course. Since GP is AS Level discipline, you are expected to attend classes only for 1 year. However, you get to study for whole two years if you are from Nepal. What you should understand is that, still after the two year course the GP result in average is not good in Nepal. Why? Because of problems with English as it is a second language for us. Not only us but all the international students whose native language isn’t English face similar problem. And language is not the only concern of GP; you should be good at content as well. Therefore, you should begin preparing for your General Paper right from the beginning of your Advanced Level (A Level) course if not sooner.
A complete guide to GCE A Level Students of General Paper