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

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

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.

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.

I'd recommend switching to organic products for your shampoo and conditioner, and to look in to preventative medications like Finasteride and Minoxidil which has been proven to halt and even reverse hair loss.  PRP would also be an option for you. Before starting any medications it is best to check with your physician.

Most probably you have a androgenetic type hair
loss. I dont advice to use finasteride because of
possible side effects and being under
the necessity of using that chemical for almost life long to stop hair
loss.You may start to use minoxidil %5 to thicken the crown area and stop hair
loss.You would better planning to have an
exam at hair loss expert for hair restoration surgery when you fell
uncomfortable about hair styling or total loss of hair..

If you are a male, then tha approach is very different than if you are a female. Please let us know as the evaluation is very different