David reigned for 40 years (5:4). He made Jerusalem the capital (5:6-12). God makes a covenant with David, see Psalm 89:3, 4, 27-29, 34-37. It was the beginning of an eternal dynasty of kings (7:16).
David was fervent about everything he did. He was devoted to and listened to the Lord (for example, see 2:1; 5:19; 7:18-29). He was a fierce warrior (both 1 & 2 Samuel have many accounts of battles he won). He was exuberant when he celebrated (6:5 & 14-15; chapter 22). And he grieved deeply (12:16-17; 18:33-19:4).
David's adultery with Bathsheba and death of Uriah (11:1-27) lead to many problems later for David and his descendants (chapters 12-21).
Many of the Psalms were written by David.