Place your hands on Parallettes , so that your head can go lower than the hands on the way down, to get into a deeper position.
Bend your elbows back (avoid letting them flare out) and lean forward while going down.
Adjust the distance from the wall and the forward lean so that your body stays fully straight the whole time (but not vertical).
It is common the arch the back, especially on the way up; try to correct that over time, as it is a compensation pattern for lack of shoulder strength.