Why do clouds usually form high in the air instead of near Earth's surface?
As air rises the moisture in it slowly reaches its saturation point and when this happens, tiny crystals of water start to condense and form clouds.
This process usually occurs higher up in the atmosphere when the temperature drops and an air parcel starts to get saturated as it rises. When all the right conditions are in place, the small crystals of water start to condense out and clouds form. See pic.
However, low level clouds can form on the ground, but only when vampires are lurking around!! Kidding of course.... "Fog" is a low lying cloud that will form if the temperatures and water saturation conditions are right.