Don't squish them down while they are cooking, you'll squeeze the juice out of them. If you want the middle not to puff up, squash it down more than the outside edges before you cook it.
I toss in whatever spices are available (Montreal Steak Seasoning is good, but I've done garlic, salt, onion powder, mesquite rub, 7 spice, whatever sounds good from the spice cabinet).
And I'm not exact with size, I'd never bother to use a scoop or measure, I just grab a handful, form a rough patty, and cook. We get hamburger (and other beef) from my brother, and it comes in 1 lb tubes, so about 1/4 of a tube is close enough.