First: Use ground hamburger meat to form your own patties as the pre-made patties tend to dry out and don't have as much flavor.
Second: For juicier burgers add a wet ingredient like 2-3 T Worcestershire Sauce, BBQ Sauce, Terriyaki, etc...
Third: Feel free to add extra flavor to the burgers with Salt and Pepper, Garlic, Diced Onion, bacon bits, cheese, etc...
Fourth: When forming the patties try to make the inside flatter and the outside fatter so that the patties have a slight bowl like shape. The inside of the patties tend to cook slower then the outside so if the inside is thinner then the outside it should help it cook more evenly.
And finally: Don't over cook! The burgers need to cook through so as to avoid foodborn illness, but you don't want to char them since that will just make them dry and chewy. Cook them for around 5 minutes on each side. Feel free to cut into the center of one of the burgers to check for done-ness. If the center is still pink then cook an additional 2-3 minutes and check again. Otherwise if the center is cooked through take them off and serve them quick so they don't dry out.
Now enjoy this tasty summertime treat!