1. Be the first to knock
Try to put together two matched melds plus four or fewer unmatched low cards. There's often not enough time to make three melds.
2. Form triangles in your hand
A card triangle (for example 4 of hearts, 4 of spades and 5 of hearts) gives you the best possibility to form a meld in the future. Develop a hand consisting of melds, a triangle, and a knock cache (low cards) as early as possible.
3. Draw from discard only for melds
As a general rule, draw from the discard pile only to complete or add to a meld, rather than forming a combination (two cards that would create a meld in the future).
4. Middle cards are better
The most useful card in this game is the 7. It works in more combinations than any other card. The least useful cards are the Ace and King.
5. Don't wait for a card inside straight
Never try to fill an inside straight in Gin-Rummy. For example, if you have a 4 and a 5, you can add to this with either of two cards, a 3 or a 6. If you have a 4 and a 6, however, you're half as likely to pick up a 5.
6. Throw the big cards early
If you start with four (or more) unmatched 10-point cards in your hand, start discarding them immediately, regardless of the combination chances. It is good to keep one high-card triangle early on, but if it is still unfilled after six or seven draws, start discarding it safely. More points are lost more quickly by disregarding this rule than by any other failing.
7. Knock as soon as possible
Knock as soon as you can. You may not make Gin, but you're more likely to pick up points from your opponent's unmatched cards.
8. An undercut is better than getting ginned
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If you are faced with the choice of the risk of an undercut on your knock or the risk of discarding a card that gives your opponent gin, knock. Your opponent is more likely to gin than they are to undercut, and the loss when they gin is much greater than the loss when they undercut.