For me personally, what I did is palmed 6-10 cards at a time... always... for practice though of course! If I had to palm 4 cards in a routine, I palmed eight! Also I held cards in palm if I was watching TV throughout an entire show but taking breaks during commercials... This helped me tremendously and improved my dexterity with the palm, because now, when I have to palm 1, 2, 3 or 4 cards, It feels so easy and natural because my hands were so used to it kind of like if you are wearing a weighted vest, when you take it off, you feel so light and natural. This worked for me! Hope it helps you!
My suggestion would be to study the videos on palming by Jason England that you can find here on t11. Additionally you might want to pick up the DVD Carney on Palming that was released a few years ago. Perfect your technique, and practice to hit palms on the off-beat rather than the on-beat, and during misdirection.