One basic piece of advice is to observe the cards your opponents are discarding; this can reveal important information about their hand & guide your own choices. An opponent might not be pursuing tha567 slots allt suit for their melds, for example, if they routinely discard cards from that suit. On the other hand, keeping cards that your opponents appear to be gathering can impede their progress while increasing your own chances of creating sets or sequences that make sense. Organizing your hand by ranking the cards you should keep according to their likelihood of forming melds is another smart tactic.