First of all I would like to recommend a great document out there - "DB Guide to Exchange-Rate Determination" which was written by Deutsche Bank in 2002 and is overfilled with FX rate determination, forecasting methods which can be used for all short term, mid-term and long term trading. If you haven't read it, look for it, download to your Kindle and take the time. It is worth. :)
In the doc several FX trading strategies are decsribed with reference to many academical writings. One of them - the Forward-Rate Bias strategy. Its results are stunning for longer term FX trading and its sharpe ratio has beaten the S&P500 two times. As the DB says: "This is the bedrock of Deustche Banks's Forward-Rate Bias trading system".
- Forward Premium and Discount
It is necessary to udnerstand what Forward Premium and Discount is before diving deeper.
Premium - Situation where the spot futures exchange rate, with respect to the domestic currency, is trading at a higher spot exchange rate then it is currently. A forward premium is frequently measured as the difference between the current spot rate and the forward rate, but any expected future exchange rate suffices.
Discount - situation where the domestic current spot exchange rate is trading at a higher level then the current domestic futures spot rate for a maturity period.
N - represents the maturity of a given forward exchange rate quote
d - represents the number of days to delivery
P - is the premium (if positive) or discount (if negative)
F - is the forward exchange rate
S - is the current spot exchange rate
- Forward Bias Strategy - Trading the Bias
"Favorite approach to trading the forward-rate bias is to adopt a diversified strategy to exploit the fact that currencies trading at a forward discount tend to outperform those currencies trading at a forward premium".
The recommendation is "going long the three highest-yielding currencies in the industrial world and going short the three lowest-yielding currencies in the industrial world. Net long/short positions are put on at the beginning of each month and then closed at the end of each month. This process is repeated each month over time". 
- Long Run Track Record for USD-Based Investors
This is truly old backtest and I would be really interested whether it can perform this good in todays market. So if there was a demand for it, I would dive into that ;o) Write a comment if you want to see it.
 Michael R. Rosenberg, David Folkerts-Landau. The Deutsche Bank Guide to Exchange-Rate Determination. 2002, Deutsche Bank.