How to make fried chicken tender and juicy?
The correct answer to any question following the template of "how do I get (some meat) to come out tender when I (some cooking method) it?" is: don't overcook it.

It's seriously not rocket science. Cooking meat dries it out as moisture evaporates. 

The second, and perhaps dominant factor is that in overcooked meat&mdash;anything above about 165 F / 74 C, all of the proteins in the meat are fully coagulated.  They have squeezed into tight little balls, squeezing out liquid, and taking on a rubbery texture.  This effect cannot be reversed.

Overcooked meat is too dry, which gives it a tough and sinewy texture.

For other tips on making fried chicken more like what you've had in restaurants (very few of which are "broasting" it), see:

How to imitate commercial fried chicken?