Thanks for posting your query.
One thing is if the dark spots are post pimple marks then you can use anti marks creams.
If they are not related to pimples
then check out if you are allergic to any food items or soaps or cosmetics.
Also be sure that you do not have a family history of skin disease and you do not have any systemic illness, since systemic diseases also would present externally.
Also use sunscreen always and drink more water and healthy diet.
I suggest you to consult a Dermatologist
if you do not find relief.
Hope I have answered your query.
Wishing you good health.