You can learn a lot about their tactics and possible melds by closely observing their draws & discards. For example, a player may be concentrating on creating particular runs or scarab slotssets if they routinely pick up particular suits or ranks. This information enables you to modify your own approach appropriately, either by obstructing their advancement or by taking advantage of their vulnerabilities. Also, you can learn more about your opponents' intentions & degree of confidence by observing their body language and facial expressions.