If you're new to lifting, you don't learn good form overnight. It takes hundreds if not thousands of reps to achieve true mastery of an exercise. If your form isn't perfect during the first month or two of your training, I wouldn't necessarily call that a terrible thing. But by the one year mark at the latest you should definitely be on point.
The truth is that you need to spend dedicated time and effort to actually learning a movement. You shouldn't be just loading weight off the bat. This is why there are so many injuries from weight training. So my recommendation is to spend your first few weeks and months learning good form. Choose a weight that's not very challenging and just see if your form improves week after week. In learning how to perfect a band-assisted pull up, for example, this might involve how to retract your scapula before beginning the movement or being sure to lower yourself all the way back down so that your shoulder blades are stabilized before beginning to pull yourself up again. Next you might want to work on proper breathing or keeping your legs fairly straight while you're performing the exercise.
Even if you're a few years into your fitness career, don't just automatically think that you already know everything you need to know about having good form on every single exercise you do in your program. Record yourself (as I did today) and make sure that your form is similar enough to a trusted professional.
You have to be fully in control of the movement at all times, not only on the concentric part, but on the eccentric part as well on the way down. Moving forward, always have the mindset that says you can be performing that movement better and listen to your body if you're feeling any pain or undue muscle soreness, which might be a sign you're doing something wrong.
Hope this helps!