The Minstermen suffered a second successive relegation to drop down to National League North after drawing with Forest Green on 29 April.
"Out of what has happened there are a lot of positives," Mills, 55, told BBC Radio York.
"Last season has gone for me, this is next season."
He added: "I've got Jon Parkin signed up for next season and 90% of the players have told me they want to play for me next season and I think that is fantastic.
"I want us to look at this game like the Community Shield and if we can win it it sets us up for the season."
Mills has previously enjoyed Wembley success at Wembley with York, leading them to the FA Trophy and play-off final double in 2012 when they won promotion back to the Football League.
Boss Mills, who has committed himself to the club for next season, gave the players 10 days off following their relegation, something he felt was "essential".
"It's a difficult time and that is when you find out about people, yourself and what this game is about," he said.
"I'm sitting here now because I want to move forward and be positive and I want to reward the fans for their loyal support after a hard season."
Should the Minstermen manage to win the Trophy they will be the second relegated team in two years to win the competition, after Halifax did the same having gone down from the National League last season.
This year's final gives Macclesfield's Kingsley James an opportunity to put some demons to rest.
The midfielder, 25, got married the day before last year's final when he was at Halifax and rushed to Wembley, only to be told he was on the bench.
"My wife dropped me off at Leeds-Bradford airport and I got to Heathrow about nine," he told BBC Radio Manchester.
"I needed to get to the team hotel so I had to pay £120 for a taxi to get there. I then got told that I wouldn't be in the team and I was on the bench.
"As you can imagine I was very disappointed. I worked really hard and played nearly every minute of every game throughout the season and then to not play at the big one was really disappointing."
James did get on the pitch for 16 minutes at the end of the game as Halifax secured the trophy with a 1-0 win over Grimsby.
York City are looking to use Sunday's FA Trophy final against Macclesfield to move on from "a difficult time", according to boss Gary Mills.