Keep your hands out of your pockets. Standing with your hands in your pockets may send several signals to those around you, probably none of them what you intend. Unless you are trying to look less confident, as if you are holding yourself back, you are bored, or you are hiding something, then take your hands out of your pockets.
Palm position. If someone offers you a handshake with their
palm down, they are demonstrating their sense of dominance or authority. Likewise, a handshake or a significant-other’s hand-hold with the palm facing up indicates they are open and more submissive.
These both sound like good advice.
And using *hand gestures* with palms up is different than laying your hands on a desk with the palms facing up. I suspect you may have misunderstood some advice or teaching material at some point and this "palms up with hands on the desk" thing got incorporated into your list of suggestions.