You should always get ready for your throwing and conditioning sessions by completing an active 5-15 minute warm-up.
An active warm-up means you are moving around rather than standing, sitting or lying around stretching. Stretching is important too, but that should be done at the end of a session or as separate training sessions.
The video below shows you a simple but effective warm-up routine for throwers. It ensures your arms, shoulders, upper body and legs are thoroughly warmed up. Some of the exercises are also beneficial for your balance and coordination.