1. Arching your back
Arching the back compresses the discs of the lower back. this is never a good idea as the low back is susceptible to damage. Maintain a neutral spine while doing pushups.
2. Improper arm position – too narrow or too wide
Placing the arms too narrow or too wide limits the amount of power you can generate in the pushup. A wide arm stance places more stress on the shoulders and may lead to impingement issues.
Wide Grip - places stress on shoulders
Placing the arms close to the body emphasizes the triceps muscles. Both wide and narrow pushups can be used as advanced exercises if you have developed the strength and mobility required for these variations.
Arms close to body - emphasizes triceps
Work with a personal trainer to make sure you are using proper form while performing a pushup.