What is your exit strategy? Can anyone give me a hint?

I think not enough discussion has been done about how to exit a trade. I am pretty discipline with cutting my loss but I am always at odds at when do I exit my trade when it's at profit.

I am currently trying to employ a take profit system to automatically take profit when the stock that I owned gained a certain percentage of profit but an acquaintance told me that it will not maximize my profit. Can anyone share how they do it or even better point to a system that I can learn for my trade?

Thank you very much!