Backache and back pain should be distinguished for this discussion, with the primary differentiators being time and etiology. Occasional back ache is often due to soft tissue injury, spinal muscle, or ligament injury. It does not involve leg pain and usually resolves in hours to a few days. The treatment is rest and NSAID meds like ibuprofen (aka Advil or Motrin).
Back pain patients have long-standing back pain, typically more than a few months. This pain may wax and wane, but it's always present. Back pain in these patients may be due to more extensive soft tissue injury or, more likely, vertebral fracture or to one or more of the intervertebral joints. Fractures are rare and are a whole other subject. Vertebral joint pain is not and is made more common by the fact that the spine has so many joints, three connecting each pair of vertebrae, two facet joints, and one disc joint. Vertebral joint damage is the most common cause of chronic back pain.
Proper posture and movement prevent back aches but have little or no role in preventing back pain. Any strenuous activity can produce muscle or ligamentous stretch and tear injuries. Lifting and twisting is an excellent example of a back-ache-producing move. For instance, lifting a heavy object and turning 90° at the waste is a good recipe for back aches or worse. Lifting, then moving your feet to turn your body rather than rotating at the hips, is much safer.
Walking hunched over is more often the result of low back pain than it is a cause. However, lifting and walking hunched over can result in back aches.
Elastic back braces have been tested for their ability to prevent injury. They don't work. Back braces with shoulder straps are no better than adjustable back braces. Firm back braces can reduce pain by limiting motion at the lumbar spine but, for the same reason, result in decreased muscle strength when used for long periods. Don't.
If your goal is to prevent backaches, learn to lift properly.