What can be done to get rid of the gray stains on my teeth? (Photo)

Thank you for your question.
Visiting a dental hygienist can remove most of the visible stains, but seeing a dentist at the same time will help any underlying causes of tooth discolouration that is not a result of staining - such as tooth decay (which also commonly appears darker that normal tooth) or inherent darkening that could benefit from tooth whitening.
Good luck with your visit -

Kind regards
Thomas Dey, BDS, MSc

I would recommend getting your teeth professionally polished. Hard to tell but this could be just extrinsic staining from red wine, coffee, tea or even certain herbs. So first is a Prophylaxis.

Dear Taylor, 
I stains which are seen on lower teeth may be due to different reasons like extrinsic stain, or may be underlying decay.. The reason for the stains needs to be analysed.. The treatment varies from oral prophylaxis( cleaning ), teeth whitening or restoration of the decayed tooth. 

Based on the photo, these stains can be from food, drinks or build up of plaque and calculus. I would recommend scheduling an appointment for cleaning, polishing, and possibly whitening. The teeth should be examined to rule out any cavities or decay.