Every player on your roster is important. Each player is important not only to the success of your team, but also to the personality of your team. A player who plays in every third game has the ability to impact your team just as much as a player who starts every game. Yes, it's true, but ONLY if they know and understand their role.
You can have superior talent, but if your team does not have a sense of togetherness then it is more unlikely your team will reach their full potential. Talent IS important to the success of a team. Some of your players have the talent to score. Some can defend the ball extremely well. Others have the talent to set up their teammates for easy scores. But how many of your players have the talent to put the team first? This is a talent needed to help any team reach their full potential.
The responsibility to get a team to understand this falls directly on the coach. How does a coach get their players to put the team first? The answer is simple, communicate with your players and help them understand their roles.
Meet with your players and talk to them about the role they have. Players may not always like to hear what a coach has to say, but there is some sense of peace for a player when they know where they stand. A player isn't going to like hearing that they probably aren't going to get into every game. Or if they are in your regular rotation they may not like hearing they aren't needed to shoot the three. But the player-coach conversation cannot end there. The coach has to let the player know that the things they can do for the team are of great value. That may be to challenge your team's point guard in practice, or to keep a particular teammate's confidence level high by supporting them. Or a player in your rotation may need to hear that their job is to set great screens, defend, and rebound. Whatever it is they have to know it is important to the success of the team because it IS important. It may not be glamorous but it is important. A player that plays their role well is a player who puts the team first.
One way to help with the communication is to periodically schedule meetings with your players. The coaching staff should sit down with each player and talk with them about their roles. Coaches cannot assume that players understand their roles. These meetings will help clear up any gray area that may be out there. If you can regularly schedule these meetings throughout your season a coach would be able to meet with each player every couple weeks.
Your team has a better chance to be more upbeat, excited about being together, and reaching their potential if each player understands their role on the team AND knows their role is important. Coaches, schedule those regular meetings with your players. It takes time, but it will definitely pay off in the end.