I could probably be accused of bias, here, but I think one of the best ways to store an oil paining is in a frame! A frame provides support for the oil painting, and also allows for you to appreciate it through regular viewing.
If you are looking for a storage solution that does not involve the art's display, I would just give you a few recommendations:
1) The art should be stored in a cool, dry, stable environment. Excessive heat and humidity place stress on the artwork, and encourage the growth of mold. Also, fluctuations in temperature or humidity can cause damage to the artwork, as the substrate expands and contracts underneath the paint layers.
2) The art should be protected from physical damage. Many stretched oil paintings become damaged from objects pressing into the canvas, or frame suffering a blow to the surface. This will probably involve storing the canvas in a strong box, with extra air space to insulate the art from pressure on the packaging.
3) Avoid placing anything directly against the face of the canvas itself. Oil paint can easily adhere to many surfaces. If this is unavoidable, use a glassine tissue intended for this purpose to prevent adhesion.
4) If the oil painting is very valuable, you may want to entrust its storage to a professional. There are a number of art storage services available that will properly package and store the artwork in a secure, climate-controlled environment.
