ESI Chart, page-253

30 years of trading and investing is one source, the other is charting inputs, watch your fibs, MACD's, bollinger bands etc.
You will get more and more familiar with moving averages, candle formations etc over time.
One usually goes through phases of certain indicators which work well for a while until they don't and then one extends ones knowledge further.

Once you get the technical side down, it comes to instinct and a cool head, stay unemotional and be ready to part with yoru shares at any given time, mostly there is ample opportunity to buy back in, but even that does not protect you from paying lessons again and again. There are just more successes woven into the story eventually.