Erase pips. Go through one of your decks and look for cards that you wish to alter by removing pips (the symbols on cards that denote number and suit). Take an eraser and slowly but firmly rub it over the pip until it is completely faded off.
Physically remove pips. It's a much better idea to use professionally printed pips than drawing your own, which no matter how good will not perfectly match that which is on the card. Playing cards are generally made of three layers--the face side, a layer of cardboard, and then the back side. Fold and bend a card from which you wish to remove a pip until you can see the layers splitting. Then remove the face layer, keeping the pip as intact as possible.
Cut the pip out. Take the removed face layer and cut the pip out of it as close as you can to the pip. Leave a little bit of white around it, just enough so that you aren't cutting into the pip itself at all.
Glue the pip to the new card. Apply a thin layer of glue to the card you wish to apply the pip to. Place the pip on the card, making sure that there are no folds or bubbles underneath it.
Draw a small circle of the appropriate color ink on each pip on a given card.
Smear the ink off of the pip. Take your napkin and lightly drag it over the ink.
Repeat Steps 1 and 2 until it you get the desired design. It usually takes more than one pass to get the results you are looking for.
Cut off an area from a card that is a little more than what you wish to paste onto another card.
Bend and fold the cut off area until the card layers separate.
Peel off the layer that you wish to apply to the card.
Glue the layer on to the card you wish to apply it to. Apply the glue to the fully intact card. Make sure that there are no folds, bubbles, or glue globs that will give your trick card away.