A very worthwhile question, as exit strategies are both important, and overlooked. As Mark Douglas writes in Trading in the Zone, one of the habits of a consistently profitable trader is paying yourself as the market makes money available.
To a certain extent, the best exit strategy depends on your trading strategy, and your time-frame. When I was trading compressions on the GBP H1 charts, for example, I was looking to capture brief, explosive moves. Fixed targets are very good at this, but they are also quite unforgiving; getting too greedy means losing everything. So, each month I would review my trades and re-calibrate stop, entry, and profit levels to stay in tune with the market. Most months, this was a modestly profitable approach.
On moving up to the D1, and expanding the range of currencies traded, this approach was too cumbersome. Each pair wanted different settings, and news events (both scheduled and unscheduled) can extend or retard the expansive movement I am looking to capture on the larger time-frame. I therefore divide each position into two orders. The first order has a modest fixed profit target, while the other order simply uses a trailing stop based on the ATR. This lets me lock in some profits early, but also gives me a chance of capturing a longer movement.
I did look seriously at using a fast moving average to close out trades (as suggested by @tommor), but time-zones mean that I’m typically managing my trades an hour or two before the candle closes. The high/low of the day is pretty clear (and if it isn’t, then the trade is moving in my direction anyway), while the close is still uncertain.