I have thinning at the crown of my head. How do I get it to grow back thicker and better? (Photo)

Exclusive of hair transplants there are several adjuncts that are effective at halting hair loss.These include Finasteride ,Minoxidil ,Low Level Laser Light and/or PRP(Platelet Rich Plasma). The most important first step would be consulting with a Dermatologist or experienced Hair Restoration surgeon in order to diagnose your condition.

You can give a try to Minoxidil and finasteride to have some thickness for your hair. Those are very good supplements for your hair.

The number one first step I recommend is a comprehensive consultation with a hair regrowth specialist who will perform lab tests to determine the underlying cause of your thinning.  Without labs, no-one can really know what your true cause is and any treatment will be temporary at best.
I would recommend finding a hair regrowth specialist who will perform a biochemical and genetic test to determine your personal cause of hair loss and then create you a personalized hair regrowth program that includes a money back guarantee on regrowing your hair.