Fremantle was aided by injuries to key Lions Jonathan Brown and Brent Staker in its round-one win, sneaking home by two points at the Gabba after an opening round defeat looked likely.
Sandilands said the side should improve this week against the Cats, after a host of key players started the season following interrupted preparations.
"We didn't play our best footy on Saturday night, but we've put a few things in place now that we've been working on through the week," he said on Thursday.
"Hopefully we can come out and play a bit better footy. We're going to have to do that if we're going to beat Geelong."
Key midfielders David Mundy (groin), Stephen Hill (shins) and Nat Fyfe (illness) were restricted in the second half of Fremantle's pre-season, but the trio hit the ground running against the Lions.
"They'll definitely be better for the run," Sandilands said. "They're all quality players and they're going to be amongst it early."
Sandilands started his season with a commanding 41 hit-outs and 22 possessions against the Lions, and he is in Geelong coach and former Fremantle assistant Chris Scott's sights this week.
Scott said the Cats would use "unexpected" tactics to combat the dominant ruckman, with Fremantle coach Mark Harvey reminding the umpires publicly on Wednesday to keep an eye on the ruck battles.
Sandilands, who was unconcerned by tactics used against him, said the midfield would be a key battleground on Saturday night, with Geelong unlikely to suffer too much from former star Gary Ablett's absence.
"They've got a huge amount of talent in their side, so I don't think they're going to miss him a massive amount," he said.
"There's a lot of players that'll step in to fill his role. They've got a great midfield, so we're going to have to be on top of our game in our midfield to win the game."
Last year's finals exit still burns at Fremantle, with Harvey this week saying his players should draw on their 69-point loss at the MCG to the Cats.
Sandilands, who played injured in that game after a clash of knees in Fremantle's elimination final against Hawthorn, said he had unhappy memories of the club's sixth finals match.
"We were disappointed with the way we played Geelong in that final last year, and losing the game, it really hurts," he said.
"I was just disappointed that I couldn't help the team out as much as I would have liked to have. It was a big game for us and that game finished our season.
"(But) it's a totally different season this year and we're really looking forward to taking them on."
Saturday night's match will be Fremantle's annual Purple Haze game, with the club raising money for the Starlight Foundation.
Starlight ambassadors Sandilands, Chris Mayne, Garrick Ibbotson, Byron Schammer and Matt de Boer, who has replaced Jayden Pitt in this week's side, were at Princess Margaret Hospital on Wednesday to launch the match.
Aaron Sandilands is a $406,500 ruckman in the Toyota AFL Dream Team competition
