1) Don't over fill the tank to much. There will always be a fill level printed on the tank outside. Never go above this and also make sure you don't go below it or you will place strain on the coil.
2) When filling the tank, don't place the liquid in the middle were you suck on it. Try to get the liquid around it so that it fills up on the sides.
3) Try not to make the tank stand up upside down for long periods of time. This will cause all the liquid to get inside the middle bit causing a major flood.