Even though times are changing and becoming more informal, it is best to err on the side of formal rather than informal. Use the formal form of “you” (usted) when you don’t know the person well. Gentlemen can be referred to as Don or Señor (Mr.) and ladies as Doña or Señora (Mrs.).
At the same time, informality is common and acceptable because Dominicans are very open and sociable people. The term amigo (friend) and hermano (brother) are frequently used. Don’t be surprised if you are referred to as mi amor (my love) or cariño (dear) in the street or in local businesses–that’s just how Dominicans communicate.