The Royals were relegated with three matches to spare following their goalless draw with QPR on April 28 and are seeking an immediate return to the Barclays Premier League.
Mariappa spent six years in the Championship with Watford and knows the matches will come thick and fast.
"The Championship can be a relentless league - it's all about recovering and preparing for the next game," he told the club's official website.
"There are some very good sides in there and I feel like the quality is improving every year. Next season will be a very tough year, but we'll be ready."
Reading replaced Brian McDermott with Nigel Adkins in March, but the club already appeared doomed to relegation.
Mariappa has urged the Royals to keep the squad intact to give them the best possible chance of returning to the top flight.
"The more you play with people, the better relationships and understanding you have with them," he said.
"But there's lots of competition for places and I wouldn't say that anyone has a position nailed down.
"Obviously you want to keep your best players at the club, and we've got a lot of good players here.
"We want to keep everyone together so we can have a strong season next year and hopefully bounce back - that will be the aim."