Despite returning to the playoffs, the Dallas Mavericks still have some work to do in the off-season. Here are five things to watch for:1 Sign their own free agentsStarters Dirk Nowitzki and Shawn Marion will become free agents this summer, as will key reserves Vince Carter, Devin Harris and DeJuan Blair. The Mavericks must open up the checkbook to retain the services of these five key veterans. Second-year center Bernard James also will be a free agent.2 Monitor point guard LarkinThis is a big summer for point guard Shane Larkin. Last year Larkin’s rookie season was interrupted when he fractured his right ankle while trying to show off by dunking in practice in the presence of coach Rick Carlisle and owner Mark Cuban. That cost Larkin summer league, training camp and the first 10 games of the regular season.3 Acquire a marquee playerTwo years have gone by and the Mavericks still have all this salary cap space, and they still have yet to sign a big fish to pair alongside Dirk Nowitzki. And time’s a wasting. The 16-year veteran said he probably has only two years left to play at an elite level. Tick-tock. Tick-tock.4 Expand Ellis’ gameCoach Rick Carlisle is convinced guard Monta Ellis can make a “quantum leap” in his game, and he’s going to help him make that leap. He was the only Dallas player to play in all 82 games. While Ellis used his quickness to get to the rim, Carlisle thinks he’ll become a much better player once he becomes an effective perimeter shooter.5 Stay defensive-mindedBy hook or by crook, it’s imperative that the Mavericks enter next season with a much better defense than the one they put on the floor this season. The Mavericks’ perimeter defense was so suspect — not counting Devin Harris — that it put immense pressure on the interior defense. The Mavericks allowed 102.4 points per game this season.