Former England boss Allardyce replaced the sacked Alan Pardew on Friday with Palace just above the relegation zone with the third-worst defensive record in the Premier League.
"We have a very important job of stopping the goals going in at the other end," Allardyce, said in a video on Palace's website (www.cpfc.co.uk).
"Attacking players when you are in possession are fantastic this season. The strengthening in that area by the club and by Alan has brought a lot of flair to the team and I think that has brought quite a lot more goals.
"But the other side is that when we are not in possession we have got to stop conceding and make sure that those goals we score win us games. It sounds simple but it's not that easy."
Allardyce is seen as one of the best managers in English football when it comes to surviving a relegation scrap.
The experienced 62-year-old was available to Palace after his short reign as England manager ended after just 67 days in September following comments he made in a newspaper sting about "getting around" FA rules on player transfers.
Allardyce is hoping to bolster the squad by signing some players in the January transfer window.
"We are certainly trying to make the squad a bit bigger with more strength in depth," he said. "The players here are good enough but if we can add to that let's try and do it."
Palace have been in the top flight since 2013 but only one win in their last 11 league matches has seen them slide into danger near the foot of the table.
They are fourth from bottom, one point above Allardyce's former club Sunderland, ahead of Monday's match at Watford.
(Reporting by Martyn Herman; Editing by Ken Ferris)
