5 min google it seems turns up the how was it done on any trick illusion nowdays.

Just give a fake explanation

for example, if you just found their card tell them that you memorized the order of the cards.

if you vanished a coin, just tell them that if you imagine and belive that the coin is gone it really dissappear.

if you made any kind of prediction, tell them that you used hypnosis to secretly suggest the card, the object or whatever you just predicted

However these are just cheap examples, it's up to you if you want to use them

This may just be the best answer in the whole thread. (That said, I know I still have several pages of posts to read, since I'm quoting something on pg.1 of 7. But the bar has been set, and it's high.)

If you aks me, this is actually a good idea for patter during the trick.

Just starting out doing magic, I've recently learned the general suckiness of revealing the secret of a magic trick to a a couple of friends. Not a mistake I'll be making again for sure, and these are some really great suggestions, so thanks, folks!

Good for you! Telling them is disappointing them.

I tell them this and it works everytime, keeping the audience entertained:

Audience: So how did you do it?
Me: *Keep quiet*
Audience: Did you do this or is he also in on the trick?
Me: Do you really want to know how I did it?
Audience: Yes, tell me!
Me: OK I'll tell you but you need to keep it a secret
Audience: Ok I won't tell anyone
Me: I did it... *pause*
Audience: Yes?
Me: With magic!

...other times I just tell them I'm an alien

Sometimes it is fun and entertaining to hear some of the theories that the audience has about how a trick was done. I was performing a Silver Scepter routine and one kid thought that there was a remote control for the wand in the case that I was spinning. The rest of the audience agreed with the theory. So, I entertained the idea and had the child spin case for me. It was entertaining watching them searching for a secret button while trying to spin the case. I had the audience where I wanted them. I maintained control of the situation. Everyone had fun. And no secrets were revealed. The whole purpose is to be entertaining. Showmanship is much more difficult to learn than the secret to any trick.

I recently discovered some of the work of Tommy Cooper. A brilliant British Comedian that knew how to work the audience. He died on stage in 1984 during a live televised performance and the audience was laughing and applauding, thinking it was all part of his act. He used magic tricks more as props for his comedy, doing most magic tricks so poorly that it became slapstick and often exposed the secret. The oaths to most of the societies make their members promise never to do things like that.

The interaction with the audience is what you want. Someone asking, especially any boy over 10, is normal. I would be more inclined to tell them something more positive. "I have been sworn to secrecy. I cannot tell; however, I can tell you that the secret to many wonderful magic tricks can be found at your local library." Encouraging them to pursue their interests, or read books.

Revealing a trick takes out the amazement of them as well. That being said it is hard to fend from the peer pressure.

Perfect. People respect sincerity.
When a spectator (and even other magicians) ask "how you did that", that's their way of saying that they really liked what you showed them. A simple smile and a "did you like that?" is my typical response. When they say "Yes", I thank them or ask if they would like to see another. At which point you can move into your next trick or tell them when and where you'll be performing next, etc.

One of Micheal Ammar lines is. if I tell me then I have to kill you.

I think the personality you create for your magic should dictate your response. For example, if you play the part of someone just fumbling through magic like Dave Williamson, then continue with that approach in answering the "how did you do it?" question with an answer like "I have no clue." This sort of response would work well for someone like Aldo Colombini.

If you are a bit more sophisticated in your presentation, like Michael Ammar who is casual, but not playing the part of a fumbling clown, then a joke like "I could tell you, but I'd have to kill you.", followed by a laugh and moving on to something else works well.

Think about different magicians, what their personality is, and how they might answer the question. Then think about your personality and how you might answer it.

I think that one thing that most good responses have in common is they tend to be more humorous than serious.

KJ

Depending on the situation I've taken advantage of my surroundings, which can work especially well with card tricks. If someone is wearing glasses, or a window or reflective surface nearby I'll drop hints that I was just looking at the reflection. Then I try to followup with something that's obviously not helped at all with reflections to add to the mystery.

Or I'll also tell them I can feel the ink on the cards, using the nice little method of peeking at the face of card with the back held to you. I've literally had a group of people all feeling cards, to see if they could do it too. After they gave up and asked, "Is that really how you do it?" I'll just go, "Nope." and that's usually enough to end it.

But as others have said it needs to be done in a friendly manner. You want to fool them, not make them fools.

If someone wants you to tell them how something is done, just tell them you accept PayPal lol :p

I can't help sometimes stealing a line from Burt Wonderstone. I lean forward and conspiratorially whisper "It's partially deboned."

It makes no sense most of the time (imagine that with a card trick), but they tend to drop the subject afterward.

-Tom

Brilliant, Rook!

Occasionally if you do the trick when people are around they might catch you. When they think they know some of the sleights they ask for the rest of the info ont he trick I never give it to them. If you give them your secrets you lose all credibility and they will find your tricks bothersome in the future. I have learned that with my co workers. The one sI alwsy try out new tricks on find me annoying, but the ones I usually don't see often after I have mastered a trick pretty well find me pretty entertaining.

Especially with card magic, I always pretend I'm showing them how the last trick is done and move directly into another trick. Gets them every time and they love it.

I have to admit a few students figured out the disappearing water cup Monte and all I could do was shrug.

From one of the greatest magic books/authors Henry Hay,he quotes John Mulholland, 1. I promised not to tell or 2. Well I do it mostly with wire's and mirrors,I sometimes surprise myself.