hmm depend on your style and strategy. If your trading around resistance lines then then you could use fibo retracements to plan where to get out if it doesnt go your way. Your stop must also be money management based. If your only trading 2% of your account per trade then the stop should limit the trade to that loss.
If you want to run profits in a trending market with high volatility , your stops have to be very far below major support or above major resistance.In choppy markets stops can as little as 8 pips in eur usd , all this depends on method ,volatility ,objective and context.