The best approach to betting the over/under in basketball is to look at the pace of play. If it’s two offensive teams, it'll likely be a run-and-gun, high-scoring affair.
If it’s a back-to-back situation for one of the teams, they could be tired and struggle to score. Or if one of the teams is strong defensively and has the advantage of being at home, they may dictate the pace and keep the game low-scoring.
Try to examine what you think the game flow will look like, which will help you predict either an over or an under.