I have used EMS scripts in DesignBuilder (DB) previously and relied mainly on four sources:

1. Design Builder help and now there is this helpful DB EMS demo tutorial.
2. A webinar recording on Advanced EnergyPlus Modelling with DesignBuilder EMS.
3. There are some EMS program examples in DesignBuilder that would be good way to start specially if they are close to what you are trying to model.
4. Since DesignBuilder uses Energyplus you may want to refer to the Application Guide for EMS as well.

These sources should be helpful to get you started.