When the medium/long term bias for a currency pair, commodity or stock index is either bullish or bearish, as can be ascertained from the daily trend table (i.e. http://fxcharts.net/category/trendtables/ ) an EA can be attached with that particular bias in mind.
CURRENT BIAS: Short EURGBP
In the example below, we currently have a bearish bias on the Euro against Sterling (i.e. short EurGbp), given that both the weekly and monthly charts are pointing lower. Note that in the short term, the charts are actually pointing higher for this cross, allowing us to sell into further strength, if we see it. We have therefore attached the Tomi Trader EA to MT4 with a bearish-bias only, to EurGbp, so no buy orders would form part of this strategy, except for when taking profit on a short position.
As and when our bias changes, we can either close down the EA or, more likely, adjust the settings to either a 2-way bias (i.e. buy and sell) or to a buy only bias if we think the market is going to reverse in the opposite direction.
The settings are very flexible, as not only the directional bias can be changed but the number of points between trades and size of the profit margin and the trailing stops can also be altered to suit your own style.