The double lift is the first trick you need to learn to learn.
Use an entire deck while practicing.
1-Hold the deck like you are dealing the cards out.
2- Grab the first card, while doing this also grab the second card.
3- Flip these cards over, but try to keep them together and not show that you have two cards.
4- After showing the second card, pretending its the top card, flip them back over.
5- Practice until good enough to show.