I could not find any Invocations to Demeter that I really liked, so this is another which I have written myself.
Hail wise mother!
Goddess of harvest
and all growing things
let your strength become mine
O'Demeter I call unto you!
Awaken within me
the power to persevere
Great Demeter, life cradled in your bossom
let your maternal love embody me
O'Goddess I call unto thee!
Bring into me your wisdom
Lady of Life
Lady of Death
Great Goddess of Balance
I honor thee Demeter
and unto you!
Into my breast I take your pain
Into my heart I take your joy
Great Demeter, My Mother
Come unto me!
O'Goddess I call unto thee!