The single most important thing you have to do when developing a trading system is to make sure you test it accurately. While there is no guarantee that a well developed strategy will perform well in the future, you don't want to start with a lie.
You have to use Look Inside Bar Backtesting or test on a lower timeframe.
In the video below we show you the difference of a strategy that does not use Look Inside Bar backtesting and how it really looks when tested correctly.
Its easy to trick yourself when developing trading systems. Make sure you have accurate backtests.