How to play Canasta well once you know the rules: the decisions that matter, and the habits that win.
Taking a big pile is how hands are won. It gives you dozens of cards to meld and removes them from your opponents' reach. Most decisions in canasta come back to one question: who is going to take the next pile?
Keep natural pairs in your hand, rather than melding them straight away. A pair in hand is what lets you take the pile when a matching card is discarded, and it is the only way to take a frozen pile.
Discarding a wild card freezes the pile, so it can only be taken with a natural pair. When the opponents have melded and the pile is growing, freezing it makes them much less likely to get it, and gives the side holding more pairs an edge.
Black threes are the other defensive card. A black three on top of the pile blocks the next player from taking it, so save them for the moment the pile is large and your left-hand opponent is likely to want it.
Every card the opponents have melded, and every card they take with the pile, tells you what they can take next. Avoid discarding ranks they have on the table, since any one of them lets them pick up the pile.
Safe discards are ranks they have discarded themselves, and ranks where you can see most of the cards. Late in a hand, count: two decks means eight of each rank, so if six sevens are visible, a seven is hard for anyone to use.
Your side's first meld has to reach a minimum that rises with your score. Early in the game 50 points is easy; once your side is past 1,500 or 3,000, you will need to hold more cards back to open, and the side ahead can find itself unable to start.
Wild cards help reach the minimum, but a meld can hold no more than three, and never more wild cards than natural ones. Opening with a meld that uses wilds is often worth it to get your side started.
A natural canasta is worth 500 and a mixed one 300, so push melds toward seven cards and keep them clean of wilds when you can. Your side needs at least one canasta before anyone can go out.
Going out ends the hand, and the cards left in the other side's hands count against them. Go out when you are ahead on the table and the opponents are holding a lot of cards; wait when your side still has melds close to a canasta. Ask your partner first — they know what they are holding.