My tryst with the Indian stock markets

I began trading on the Indian stock market (NSE) in October of 2005. I was acting as a money manager for an FI (actually on behalf of my brother Aseem living in SF, CA :))

My experience till now is a mixed bag of feelings. I am happy about identifying stocks which had the potential of growing - I bought them low and sold them high. But after I sold them I realised that I did not sell them "high enough". The more I look at the current prices of those stocks (for example: Phoenix Lamps, Balrampur Chini, Mastek) the more I have a feeling of incomplete satisfaction, i.e. I could have gained much more.

I don't know whether I need to be more scientifically driven to determine the price at which I should sell a stock, or is it just that I need to generally patient with things (I am a bit impatient and impulsive)?

Any comments or suggestions?