The gluteal machine will work your glutes directly. Stiff leg deadlifts will as well.
Remember: think through the motion in your head. Once you put your thinking cap on, you'll be able to figure out much of this on your own.
Heavy squats will make your butt big, especially if you hunch over doing them.
With regard to form, that's a commons sense thing, really. Stay in control of the weight; go through a full range of motion. On squats, however, my orthopedic surgeon friends tells me not to break parallel (do less than full motion) because of the bursa in your knees and the way breaking parallel taxes that bursa. Look at the anatomy of your knee. I've been fortunate in that in 32 years of lifting, I've never had any knee problems. If you are going to do full motion squats, I'd back off the weight some. Main thing about form is that it's common sense. Your proprioception should develop as you go along, and that'll help.
If you work your legs, you'll develop proportionately, and your butt will come along. Having a big ass and tiny legs seems silly.