What game are we playing?
In general, don’t react with noises or expressions on your face when you look at your cards or pick a card. Know your cards well enough that when you pick a card you can do your turn quickly. lf you take a lot of time it implies your hand is good, and you’re having trouble deciding what to throw. That’s for games like canasta and rummy. Still, be careful. It’s better to pause than make a fatal error.
If you have a system when you hold your cards, like you put wild cards on the right, change that up to the left sometimes. Sometimes, it’s good to keep cards up in your hand, and put more down at once so your cards are a mystery to your opponent for a longer time, but it depends on the game.