I don’t set hard and fast “numbers” to buy and sell. I watch what the price is doing (trending up or down) and then also look at the fundamentals. I usually buy little bits at a time, but when I sell it’s usually at least half of my holdings. If it is a stock I really like, I never sell it all. I keep some for more trading. If I don’t like the prospects of a stock, or it does not look like it has too bright of a future, then I will sell all and get out of it.
Good luck to you,