Eye movements are unstable by definition and there is also noise added by the system, so an unfiltered or lightly filtered gaze data signal is not ideal as a way to control your mouse cursor all the time. There are also “Midas touch” and “mouse chase” problems. For further reading, refer to this paper, especially chapter 4.1.3 Problems with Eye Gaze as Pointing Device.
If you want to try this anyways, you can try to use one of the fixation streams (slow or sensitive) provided by the EyeX Engine. However, if you want to have full control of the parameters you should do your own smoothing algorithm. One easy filter that is quite efficient is a weighted moving average filter, for example the exponentially decaying filter discussed in this StackOverflow thread. For further reading, this paper includes a good summary.