When playing Rummy, you can only put down a combination during your turn. The correct timing is to pick up a card from the stock or discard pile, put down your meld, and then make your discard. The advantage of putting down a combination before you’re ready to go out completely is that you reduce your exposure if you lose the game. However, you do run a few risks by putting down a run or meld.
The disadvantage of putting your cards on the table is that any player can now add to your meld of three of a kind (by adding the fourth card) or extend your runs. Although adding to your combinations proves very beneficial to your opponents, the longer the game goes on, the more wary you should be of keeping melds in your hand.
Conversely, you can add to your opponents’ combinations — or, if you draw the right card, you can add an additional card to your own melds. If you want to add a card to an existing combination, put down any combinations you have, add to the existing set or run, and then make a discard. Your turn finishes with the discard, so make sure that you don’t mix up the order of events. If you do, you can’t put down any combinations you may have until your next turn.
If you put down an imperfect run, you simply pick up the cards and put them back in your hand. But by revealing the cards in your hand to everyone else at the table, your chances of getting anything useful from the other players decrease. Better put on your glasses and double-check before laying any cards on the table.
When you have a set of four of a kind, no card can add to the combination, if you are playing with a single deck of cards, so you’re safe to put these sets down immediately. The only reason to hold them is if you’re close to going out and you want to play for the extra score. Additionally, if you can possibly use a card in the set for a run, you may want to retain the combination in your hand until you know how you want to use the cards. For example, you may want to hold some of the cards in the following figure until you get some more information.
In this figure, you could use the 9 of Hearts both in the set and in a run with the Ten and Jack of Hearts. Holding the cards for a turn gives you a chance to pick up the Queen of Hearts or 8 of Hearts, which would improve the run.