One of the things I see with a lot of swimmers at meets is that they waste time with their backstroke starts by tucking the chin into the chest and curling up like a spring ready to shoot off the wall.
The most recent scientific research on the best form for a back stroke start show that a straighter back with the swimmer imagining that someone is pulling them up out of the water by their hair. This means the head position is more open with the arms doing most of the work to hold the start position.
Added to this feet are placed at the same level almost as high up the wall as possible. In fact, if you watch a lot of the top swimmers they may even have their feet and backside out of the water. Further, top swimmers do not place one foot above the other, which is taught in some swim schools to stop slipping on the wall. By having one foot higher than the other you cannot generate the same power off the wall.
Gary Hall Sr. demonstrates the backstroke start really well in the video below.
Enjoy, practice, get better.