Casting varies too much by system usually.
Might I suggest the item must have a blood stone or a crystal that shifts from red (full charge) to clear (empty).
Might I also suggest that the item should be used in the casting as a "pointy wavy" thing so it is obvious that it is the foci of the power (and those items that are not required to do such, have less power per effect. )
The rest of the casting is per requirement of your game system/ world. This way the magic could easily fit your world.
I would write the system up given relative strength of points of blood to given effects. Thus a dragon's blood might provide 500 points of magic energy, while a rabbit mere 5. Then give that a small spell uses one points, a spell uses 5 usually, scaling spells multiples of 5, and massive spells 100. Or some such