Below is a compilation of YouTube videos on learning the javelin throwing technique, correcting common faults, and working on exercises/drills that one can use to prepare for the season and to improve on existing technique.  Care needs to be taken to start slow and work into some of the routines that are depicted in the videos, especially when it comes to stretching.  Initially, training sessions  should be short in duration and low in intensity, whether it be actual throwing or working on conditioning exercises.  Be patient.

This list of videos contains only a few of the ones that you can find online.  The criterions used in choosing the videos were understandability, practicality and simplicity for the thrower in training.  More and better videos are most likely out there, but these should suffice and are free.

Scott Halley’s Javelin Instruction Series on YouTube:

Topic Foot Position
Topic Preventing Elbow Injury
Topic The Penultimate Step
Topic A Whole Body Throw
Topic The Block
Topic Javelin Position and Control
Javelin Drill Javelin Position with Bar
Javelin Throw Fix Over Rotation
Training with Other Implements Instead of Javelin
Javelin Throw Practice Spring 2006
Training Throw Spring 2008
Javelin Throw A variety of Techniques

Teach PE Javelin Series with Tim Newenham on YouTube:

Javelin Coaching Standing Throw and Common Faults
Javelin Coaching Common Flight Errors and How to Correct Them
Javelin Coaching Run Up Part One
Javelin Coaching Run Up Part Two
Javelin Coaching Run Up Part Three

More Conditioning and Warm Up Exercises and Drills:

Dynamic Flexibility Exercises For A Thrower (Javelin, Baseball)
Javelin Throw Warming Up With The Implement.m4v
Javelin Specific Conditioning Session by Didier POPE
Javelin Throw Delivery Exercises by Didier POPPE
Throws Conditioning Stabilization Drills by Didier POPPE