Aside from getting young players in the draft or as free agents, the single most important part of a rebuild is developing talent. A team can select in the top ten or five every single year and still fail to get better over time. Take the Edmonton Oilers for example. That team drafted in the top ten nine of the past eleven years and have a single playoff appearance.
The emphasis on player development is tied to the salary cap implications. Before the NHL had a salary cap, teams were able to just back up the Brinks’ truck and sign veterans every single summer to fill holes.