I trade options on stocks for almost 2 years now and i do a lot of strangles and naked puts/calls. I've not done any strangles on forex nor do i intend to for various reasons.
Now, back to your question. When i trade strangles on stocks, i usually look for a couple of things. First, the volatility of the stock followed by support and resistance. I always try to pick stocks which are that volatile to begin with and i always look for intermediate support/resistance levels. Those would provide you with a mental stop on when to get out. If possible, have multiple support/resistances as buffer between your strike price and market price.
Relating to stop-losses, be careful of sudden spikes in volatility which could trigger your stop-losses even when the strike price isn't breached. To make matters worse, the fill price might just be ridiculous. My method is to have a mental stop instead of a physical stop. Coupled that with price alerts on my handphone, i normally have time to react to major events.So far, i've not had any major losses for the past 2 years of trading.