Good tips for spray painting:
1. Hold can about 30cm (~12") away from surface.
2. Spray in ONE direction only (ie. from Left to right)
3. Do not overlap lines too much. This can be done on the second coat or when the paint is touch dry.
4. For best results, keep can upright (ie. hang the bonnet from one of the smaller holes in the back of it. Make sure that the wall and surrounding ground is covered in plastic to avoid overspray.)
5. Clear-coat is a must. A good rule of thumb i use is 2-4 coats of clear-coat to every one of paint.
Try some of these tips.. They may help, but then, they may not.