Unfortunately not much, the Chromecast is not a very powerful device and the WiFi antenna in it is quite small so you may be getting poor signal resulting in slow WiFi speeds leading to buffering.
If playback is just fine on the iPad or smartphone, both WiFi devices, I would get another TV playback device. Say a FireTV or Roku. Or this new Android box which is supposed to work well with the Tablo (it replaces the Google Nexus Player as a good Tablo playback device):
What is the make and model of your router? You coul try upgrading your router which may improve WiFi signal as well.