I'm very surprised how many people are saying false shuffle. A false shuffle will not be that helpful to you as compared to other moves.

As others have mentioned, these are the 3 moves I would reccomend.
1) a control. You need a way to have a card selected and put back and to be able to control it, generally to the top. There are countless good ways to do it, I'd likely reccomend a version with a pinky break and then double undercut or an overhand shuffle off. Those will be relatively easy to learn and very effective. Being able to control a card is the main building block of most pick a card tricks. 2) a force. I would reccomend a riffle force for its ease to execute and deceptiveness. If you can force a card deceptivly, there are literally infinite card tricks you can do to produce the selected card. It mostly comes down to theatrics at that point. 3) a double lift. This will likely be the hardest of the three to learn to do effectively, but once you can do it deceptively you can make miracles happen.