Nets players may have been working out informally for weeks, but Saturday marked the official start of training camp — one they expect to propel them to a serious playoff run.

They’re laying the groundwork for any postseason success before the preseason even starts. The Nets added offensive punch, but are trying to shore up Achilles’ heels such as defense and rebounding.

“We haven’t changed a lot, but we’ve tweaked some things, so that’s always a challenge,” coach Kenny Atkinson said. “But [a] lot of teaching. [It was] good.”

It was a long first day, with the most attention paid to those two weaknesses. The longest session — a full 20 minutes, a source told The Post — was spent on defensive breakdowns. The next longest? Transition defense, at 15 minutes.

“We can take more advantage of the offensive boards. That goes with transition defense, if that makes sense,” Atkinson said. “How you’re attacking the boards, that determines what you’re doing going back. Just some tweaks there.

“Some tweaks with our pick-and-roll defense … change some things. It’s personnel-based. We have DJ [DeAndre Jordan] now, that changes some things. And Garrett Temple and Taurean [Prince]. Just understanding what our personnel looks like.”

The personnel looks a lot different. The Nets can score, but to fix flaws like their defense and boardwork, they need Prince and Jordan to step up.

“We worked on [rebounding], we have to improve,” Atkinson said.

Jordan will compete with incumbent Jarrett Allen at center. The 31-year-old finished in the top five in offensive rebounding for five straight years before finishing 11th last season — that will allow the Nets do different things when he’s on the floor.

“Sure, it’s competitive. Those are two competitive guys. The problem is they both played really, really well [Saturday]. It’s two really good players. It will evolve. It always plays itself out,” Atkinson said of Jordan and Allen. “Those guys both know they’re competing for something.”

Prince is a career 38.0 percent shooter from 3, and his stroke has surprised even the Nets. Still, with Kevin Durant and Wilson Chandler out and Rodions Kurucs facing legal woes, Brooklyn will not only need Prince to play major minutes, but get back to being the glove he once was.

“The challenge for him is to be our defensive stopper,” Atkinson said. “His early years in Atlanta where that was who he was, he was a 3-and-D guy. We’ve got the 3, we’ve got to get him to play that D.”

Prince admitted injuries — missing 18 straight games with a sprained ankle — hurt his mobility last year. Now fully fit, it’s a challenge he relishes.

“I’ve had that responsibility since my rookie year. I’ve guarded Marc Gasol, Kyrie Irving, Paul George, LeBron [James] since I got in the league, and it’s been that way every single year,” said Prince, adding, “I didn’t know coach said that, but I was going to demand that and it’s something I look forward to.”

At a modest 6-foot-8, 220 pounds, Prince is undersized at power forward. But he says experience will help him get around that.

“You have use your mind, be smart, not get into foul trouble,” said Prince. “But that comes with knowing the scouting report, knowing what the team wants to do, not being vulnerable, keeping your hands back.

“And then also it’s a team game, so everybody being in the right position at the right times, and knowing if a team likes halfcourt or transition offense and trying to limit that as best you can.”

That’s where having rim protectors like Jordan and Allen help him.

“It’s going to be great knowing I have a great line of defense behind me, guys that can make people second-guess themselves,” Prince said. “If I can just do my part, when it does get to them they do their part, that’s what being a great team is — and I think we can do that.”