Wilder, the Blades fan and former player, was unveiled as Nigel Adkins’ predecessor on Friday after United elected to part company with the former Scunthorpe and Southampton manager.
Adkins guided United to an 11th-placed finish in League One in his only season in charge, and Wilder will demand more of his players when the season kicks off in August.
“I’ve had a good look at the squad,” Wilder said, “and I have some big decisions to make but in the end, I want an energetic and vibrant team.
“I’ve had that at the other clubs I’ve been at and the players have to want to win games of football.
“Of course, there’ll be times when we have to see games out but by and large, we’ll be going after teams and going for wins.
“We have to be positive in everything we do and the players - be it ones who are staying, ones coming in or ones that were leaving that might now be staying - will have to show all those qualities.”
Wilder, aged 48, took Oxford back into the Football League and won the League Two title last season with Northampton Town, despite well-documented financial troubles.