Depends on the person. You can't put new ideas into a mind that is closed. Are they open to discussing your beliefs/practices? If so, give them some books to read and/or links to websites. If they're not willing to even have the discussion, it's probably better to not bring it up again, and just quietly go about doing what you do.
If the wont listen them don't bother trying to get them to listen they are incapable of it became they think they already understand what it is and think your being lied to about what its by some con artist or some evil individual that wants to fill you head with evil ideas
I think it depends on how do you see magic itself and how seriously are you handling it. I'm here on a Quest for Knowledge and therefore I have little intention to be a powerful practitioner. I won't stack gems, stones, amulets, even candles in my room, so there is no visual evidence of what I'm doing. There's no need for them to know anything.