Nobody wants to be monitoring the prices all day with the cursor on the sell button just waiting to click the mouse, so how do you decide when to sell?
If you set up an open order with a low target price, you'll be disappointed when the price climbs well above your target price.
If you set up an open order with too high a price, you might not sell at all.
What's your strategy?
Depends on a lot of things that all boil down to one thing: market conditions
I'll tell you, when I started I knew the key to being successful was to be flexible, but all the material I found said "Take no less than 2x risk and sometimes 3x or more depending upon the trade" I found a ton of different methods to define "sometimes" and "depending" and eventually, with no other options I gave in and found myself asking the same questions you are. Sometimes my trades would reverse right before my take profit point. Sometimes I'd take 2x profits and see it run 5x or more. . and did I ever need that money to mitigate previous losses! It was infuriating, and the none day I found myself back at the beginning learning to be flexible.
First, if you haven't accepted that you'll almost never buy on the lowest tick of a move and sell on the highest please do that now. It's all about taking your profits out of the middle. Getting better causes your middle to get wider. . . or something.
Second, I learned to lean on my experience and to know what type of market conditions I'm dealing with. If I'm in a choppy market the distance between value and weakness will be smaller.
Third (and most specifically), I found truth in volume. This is a discussion that can take up many books but to boil it waaaaay down think of it like looking at a TrueCar report. They show you a distribution of cars sold 1x @ 32,000 5x @ 35,000 1x @ 37,000 and we're helping you get it at $32,500! Right? That's value, and you can tell because almost no one is paying that little. Weakness is on the other side. No one, except for one schmuck with bad credit and no negotiating skills paid $37,000 because the price is too high. The market can't support it.
Most recently bitcoin almost hit 8k, but when it got there volume dried up and sellers came in hot and heavy. The market couldn't support it, and the price dropped quickly.
So that's how I do/did it. It takes time to learn how, but once you do you'll see it all markets.