1) Straight arm pull-overs.

The best exercise for developing the serratus anterior. It also works the pectorals and helps expand the ribcage.
The subject lies on a horizontal bench, face up, across it, with only his/her shoulders leant on it, holds a dumbbell with both hands straight up in front of his/her chest. The dumbbell should be held in a way that the subject’s palms point upwards pressed against the plates of the dumbbell. Legs are used to provide support for the lower body.
He/she then slowly lowers the dumbbell over his/her head keeping the weight under control, at the same time the lower body is also lowered a bit till the pecs are fully outstretched. Pausing for a moment he/she then lifts the dumbbell back to its starting position.
Extra considerations: - you might want to keep the hips dropped when you do the lifting. This secures extra stretch throughout the exercise.