Buying/selling at a support/resistance area with the trend and after you see a signal candle - ideal.
If you are correctly identifying a trend and entering at the right point, price won't be doubling back on you because it is continually stairstepping. However, if you see it start stalling, arching, consolidating sideways - might want to get out.
The other thing to consider is are you in a trade to ride the trend as long as possible, or are you trying to get in - make some money - and back out. The general rule I've heard most people say is shoot for 3x your risk minimum.