What should we do when we see a gain in a stock?

This is a million dollar question, give it a serious thought for this question will help you make more money in stock market. Usually there are two things people will do.
1)Sell it. But wait, what if the stock price continue to rise? We will be kicking ourselves of "selling it too early" I used to own this one stock NVDA. After I sold it for a small profit, the very next day, the stock jump over 10% in few hours trading session. I just left regret and watching it go up with no stock on hands.
2)Hold onto it. But wait, what if the stock price tumble after reaching some new high. I had an experience which the stock price go from $5 to over $18 in a short period of time. I was so ignorant, thinking the stock will hit 30 dollar soon. So, I didn't sell a single share. Well, the stock crash down after some bad news earning! Now the price is sitting around 3 bucks!
Obviously, the above 2 ways are not very intelligent ways to handle the stock when it has a gain. Now after all my bad experience, I will tell you the 3rd way to help you build wealth.
529pm: sell a portion to lock in the gain gradually. EX:
When stock has risen and reach more than 7-10% of original buying price, you should sell half of the stock to lock in your gain.
When the stock price has reached 12-15% of the original buying price, you should sell a quarter of stock to lock in more gain.
Finally, when the stock has made 20% or more advance, you should sell the remaining quarter to capture the remaining gain.
I do believe that's the best way to answer the questions on topic. What's your thought?