How to decide when to sell stocks?

KLCI closed at 1439 this week, 5% lower than earlier week. I have regretted that I did not sell GAMUDA at earlier week, it was at 28% profit but now down to 16%. You know! I have been telling myself to sell at 20% profit, so far this approach is not followed consistently. With Vietnam project worth RM10 billion and RM12 billion double tracking rail project, I thought GAMUDA share will go up further and I should sell at >30 profit..too bad, this week market selling pressure emerged with fear of US in recession.

What should I do now? sell or wait? What is the consistent way to make money from stock market?

For now, I will try to keep my approach to sell at 20% profit....don't be greedy. Also, I will close my monthly account with 5% ROI, if possible. Monthly closing account appeared to be effective as I must sell profitable shares on hand. It helps me to achieve 22% ROI in 2007.