You should have a look at Dennis’s thread here - Trading the Trend with Strong Weak Analysis.
As an alternative, check how the currency is doing against a standard currency - most people would use USD for this, but EUR would be a good option. If your currency is bullish against the USD, ask yourself some really tough questions why you would want to short it against some third currency.
Finally, each weekend I check which currencies are bullish or bearish against the most other currencies. You can use various measures for this as long as you use the same one and stock with it - that way any changes will be apparent and hopefully meaningful.