Practising rummy on a daily basis leads lets you know more about the game and thus you can then make out things and get the better of your opponents. Here is how can you do that.
Keeping an eye on your opponent move gets you an idea on which of the card he/she is behind. Look for the cards picked up by the opponent from the discard pile.
You can figure out the probability of cards of a particular colour by analyzing what colour cards your opponent is discarding.
Similarly, if your opponent picks two or more cards of the same value but different suits, they are definitely going for a set of cards of that value.
Lastly, look at the discard section closely, this will give you an idea of the cards that might be in the deck and with your opponent.