It depends -- is the spell supposed to be in the paper itself, or is the paper merely your instruction sheet?
If it's an instruction sheet (the equivalent of your recipe for cooking) then you can dispose of it in a normal garbage can, recycle it with your recycled papers, or keep it in a binder or scrapbook.
If you consider the page to be an integral part of the actual spell you have lots of choices regarding what to do with it. It is common for people to burn the paper in fire as that was a traditional way to offer something to the Gods -- basically handing it over to Them to be dealt with. Or you can bury it in the ground, or put it in a body of water (lake, stream, river, etc.) A lot of the choice depends on the type of spell you are doing and which element or deity you are hoping will effect the spell for you. For instance if you're praying to a god associated most with fire, don't put the spell into water or bury it in earth. Underworld deities and spirits probably won't appreciate the spell being cast to the winds, but prefer things to be buried in the earth or put in deep waters like the ocean.
And some spells work best if you keep the spell components close by, such as when it's done as a sachet -- often kept in a pocket, or under a pillow on your bed. It depends what the purpose of the spell is and who you're working for and with.
