Someone basic, attached to day by day issues, ruled by the common sense. Not a dreamer or idealistic, not into the creative field or the Arts. Usually connoted with one either without studies or a especial knowledge or intellectual skill. In some context you may use it to express ones singular act, but not the person them self.
I'm quite down to earth: eating, drinking, fucking and sleeping are my life.
She's too down to earth you may need to do a drawing, so she may understand.
Lincoln used to plant his own garden.
This book is really down to earth; any child can read it.