The ultimate rule of making a delicious burger: only season the outside of the burger patty. Never, ever season the ground beef and then mix it before forming the burgers. This makes for extremely dense burgers that are not great to eat. The kneading and salt just turns them into bricks. Check out this awesome post at Serious Eats for photo proof!
As far as proper seasoning: I put a TON of salt on the outside of the burgers. A big pinch on both sides, sometimes two. You need to be able to see the salt. You will lose a little in the pan while it's cooking, so don't worry if it looks like a lot.
Apply as much pepper as you like - it's not as important to the finished product, so it's just a matter of personal taste.