Where do you set them? Back testing your system can be helpful here. You can check thru the last months and years of markets that would trigger a trade under your system and work out what would have been the optimal setting for the limit order. Remember naturally that past results are not necessarily going to be repeated in the future. Testing in a demo account is also helpful. This may mean that you just need to score a 50% success rate to be in profit. Setting the limit order at twice the pips of the stop loss, either before or after spread, might be suitable. this depends on your system.

Using limit orders has another valuable benefit too. When you have both stop loss and limit order prepared you can run away from the computer and get on with your day. There is no need to watch every little fluctuation of price till one or the second is triggered. So using limit orders in currency exchange trades makes for a happier, more profitable trader.