After the dog-up, the backbend we practiced most often was the urdhva dhanurasana (wheeled pose). Do some preparatory stretching exercises before practicing backbends. The wheeled is a fairly deep backbend. Doing some preparation can help to elongate the right tissue to create space along the front of the body, more evenly along the length of the spine.
Hip flexor preparation
Start with the pelvis. The trunk is connected to the pelvis by the spine. If the hip flexors are tight, opening the muscles around the shoulder straps won't help much with the backbend. These three poses prepare for deeper backbends, with a focus on opening the hip flexors. These are excellent asanas for lengthening the hip flexors, but require a gradual deepening of the range of motion.
First Edition: Get down on your knees with your heels back. If bending your knee completely is difficult or causing pain for you, place one or a few yoga blocks between your heels and sit on them. Then place your elbows on the ground behind you and slowly lean back. Lift your hips off your heels as much as possible. Don't spread your knees too apart.
Second Edition: If you want to do a deeper stretch, put your hands on the ground. This will deepen the stretch. However, focus your attention on the lifted hips so that you can fully stretch the vital tissue, the hip flexors.
Third Edition: If you want to go deeper, there is a third version. Kneel, but put your toes underneath so your feet are dorsiflexed. Then sit on your heels and reach out your hands to grasp the majority of your feet. Similarly, lift the hips to stretch the hip flexors. It's normal to feel these stretches near the knee.
Shoulder preparation
Bridge pose is a good wheeled prep asana. The modified bridge pose does not stretch your hip flexors. But it can make a beneficial preparation for your shoulders. To reap the benefits of opening your shoulders, emphasize tightening your shoulders as if you were doing a shoulder handstand.
After preparing your hips and shoulders, check the distance from your hands to your feet, the longer the distance between your hands and feet, the more space your lower back will have. Also, don't overcontract your gluteal muscles (i.e., glutes).
If your shoulders are too tight when you do the wheel pose, you can place a yoga block against the wall. Then, place your hands on the yoga block to reduce the flexion of your elbows and shoulders.
There are also some misconceptions about backbends, especially wheels. For example, you need "strong legs" or push your legs hard in a wheeled pose. The more tension we exert on the pelvis by contracting the gluteal muscles, the harder it is to rotate the pelvis into a comfortable position. We need leg activities to improve posture. Use as much force as you can, but as little brute force as possible.
If you're just starting out with backbends, prepare for gentle upward facing dog poses before you start doing deeper backbend asanas, which require the front of the body to be longer and more open. Backbends are fun and good for opening up the front of our body. They can help us regain some balance after sitting for a long time.
If you are a beginner, please practice patiently. To start, consciously lengthen the hip flexors in an easier position, such as the upper dog or arch pose. Then, when you get more flexibility, you can add asanas like wheeled poses.