You can change the difficulty by adjusting your body angle. Move your feet forward to make the exercise easier, move your feet back to make it harder.
Avoid the lower back from arching too much and having the stomach drop towards the ground. This will cause unnecessary stress on your lower back, that might lead to back pains. Keep your body straight the whole time.
Do not keep your hips back while moving. This might feel easier, but it will make your workout less effective. If this happening, walk a little forward to reduce the stress of this exercise.
If you feel discomfort around the shoulders, try to widen the distance between your arms, try several grip positions to see what is comfortable for you.