This is a great exercise that can help to improve your posture. The rhomboid push-up helps you with your shoulder blade positioning which influences your thoracic and cervical alignment. When the muscles between the shoulder blades are working correctly the neck posture is held in place positioned over your shoulders with more ease.
Stand on ‘all fours’ with your arms and legs at 90 degrees so that your hands are straight under your shoulders and your knees under your hips. Relax the small of your back into a natural arch and keep your neck relaxed so your spine is in a neutral position that you can maintain throughout the exercise. Then drop your torso down by slowly squishing your shoulder blades together. Make sure that your elbows stay slightly bent and the elbows are pointing back towards your thighs throughout this shoulder blade movement exercise. People often confuse this exercise with the cat/cow stretch in which you arch and flex your spine, however for this exercise all the movement should happen by the shoulder blade sliding on the ribcage while the spine remains in a neutral posture.
Work your way up to 60 sec of slow controlled movement and repeat 3 times per day for best result