See how to lower the striker on a Luger P08 (Pistol Parabellum) for storage.
Always make sure there are no cartridges in the chamber!
Be sure to follow all disassembly and assembly instruction found in the technical section of http://www.lugerforum.com.
If you are not sure of what you are doing or if the gun is not working properly, take it to a competent gunsmith.
Be sure to follow all NRA firearms safety recommendations.