A player on your Dynasty Mode™ team makes the All-NBA team.The All-NBA team is compromised of 5 of the best players in the NBA for that particular season. There are 2 All-NBA Teams, so you'll have 2 chances to get this achievement.
Scoring points, getting Rebounds, getting assists, getting steals/blocks and playing good Defense will all help you to get on one of the All-NBA teams. Once again I suggest using the Boston Celtics, Los Angeles Lakers, Phoenix Suns, San Antonio Spurs, or the Cleveland Cavaliers. At least one person from all of those teams gets selected to one of the All-NBA teams.
You can sim through the season and get this achievement.