Say you want to have someone pick a card from a deck and magically find the card. You will need to control the selected card. If you can control the card they have chosen it will be easy to find.

Controlling the selected card with a key card.
If you are unfamiliar with a key card, just mark the back of a playing card with a couple of pencil dots. Small enough that you can see but your audience cannot. This can be used as  key card. So when they choose a card, you will place their card back into the deck on top of the key card that is marked. In this way you will be able to control the playing card they picked.

Moving the Chosen Card to the Top of the Card Deck.
 You can use a key card to secretly move the chosen card to the top of the deck. If the key card is right on top of the card they picked, just cut the key card to the bottom of the deck. What this will do is to naturally move the selected card up to the top of the deck. Then you can reveal that the card has jumped to the top.

Move the chosen card to the Bottom of the playing cards.
 This move is very similar to the one above. Just cut the key card to the top of the card deck. This will move the selected card to the bottom instead of the top. So once it is on the bottom you can reveal the card has traveled to the bottom.

Case Card Trick
You will need to memorize the top 3 or 4 cards. Then secretly place them underneath the card case. Now to perform the trick just take the playing cards out of the case and have someone shuffle the cards to mix them all up. So there is no way you know the order. Have them place the cards back onto the table or ground. Set the card case (with the hidden cards underneath) on top of the cards. And immediately have them put all the cards back into the case. Now you can remove the cards slowly one by one calling out the names of each of them.
Only do this trick once. They might catch on if you do it again.

Do not tell how you did the card tricks. These card tricks revealed methods should not be told to your audience. It is only amazing for them when they do not know the secret.