Here is a method:
1. Does the belief concern something real, that is, something that can be defined to be 'real' according to whatever definition of real you hold?
2. Can you reason in such a way as to verify for your mind that it is real? Can you justify your belief?
3. Is there sufficient reason to continue believing in it after much time has passed?
4. Is there no way in which you were wrong to hold this belief?
5. If you were wrong in some way, is there good reason still to believe that you were right?
6. Is there a necessity for the thing?
7. Does the thing serve a practical purpose?
8. Do you find significance in the thing?