I personally, use a discretionary approach to trailing a stop.
As said above, using lines of support and resistance (I also use both these for price targets occassionally), along with range of the bars, close and volume. Only real other thing I look at are RSI divergences. Also take note of traditional chart patterns forming as the trade ensues.
However, I am looking at trying out an ATR (Average True Range, look up Van Tharp, Korrupt) stop at the moment, based on a short period MA (maybe 10?), to take into account the rapid changes in volatility seen at the moment.
Focusing mainly on swings at the moment.
Cheers