I'm a big advocate of
German Volume Training.
Having done the program for 3 consecutive months, the sheer difficulty of this program will not only add muscle to your body very quickly (provided all other factors are optimal, i.e. nutrition, rest), but will really help to improve your form. It did with me.
The 40x0 tempo for compound movements (4 seconds for eccentric movement and as rapidly as possible for concentric movement) really forces you to have your form in check.
With the weight being around 60% of 1 rep max, I found that for the first couple of sets, I would focus on "feeling out" my correct form, and with the aid of the mirror (for squats and deadlifts), ensure that everything is moving in the appropriate direction. The reason why it's important to feel your correct form is because when you reach the final sets, you'll need to have both the discipline to maintain the correct form and while combatting the
extreme muscle fatigue. Once you know how the correct form should feel, it becomes second nature, and you'll be able to focus more of your energy towards combatting fatigue.
The fact that you're doing 100 reps of an exercise will also accelerate the learning process for how you should be executing the correct form, provided that you are conscious of your body's movement and aware of how to correct your form if need be.
I've now switched to a strength program, and all of my numbers, solely due to GVT, have greatly increased, along with my confidence in my form.