Madrid, crowned European champions in three of the last four seasons, are top seeds in a fiercely competitive group that also includes Spurs, Borussia Dortmund and APOEL.
Tottenham host Dortmund at Wembley on Wednesday and while Pochettino acknowledges the importance of his side's opening clash, he does not see it as a scrap for second spot.
The Argentine urged Spurs to make a confident opening to the campaign after failing to progress to the knockout stages in last season's tournament.
"I think Wednesday is so important, to start well in the competition and get the three points will be key to the future," Pochettino said at his pre-match media conference.
"In theory it should be Real Madrid first and the others trying for second, but football is not about theory. Our ambition is to win every game.
"Real Madrid are on a different level: they won the last two Champions Leagues so it's a different reality. I think it'll be a very competitive group.
"Last season after the first game against Monaco it was difficult to change the dynamic. It's so important to try to win the game. It will be tough, Dortmund are a great team, but in our mind our mentality is to win and be aggressive from the start.
"Last season was our first experience in the Champions League... It was a very painful experience because we couldn't be at the level we needed to be, but now that's not an excuse."
Pochettino feels Spurs must take up the challenge of rising to the level of Europe's top clubs after finishing second in the Premier League last season and third in 2015-16.
"Now we need experience," he said of their attempt to match the likes of Madrid.
"We need to challenge them. Remember - we had to reduce gap to the top-four sides, now we're fighting again to reduce the gap with these type of clubs in the Champions League.
"This season will be a very good season for us to challenge them and show our reality."
Asked whether recently arrived defenders Serge Aurier and Davinson Sanchez, signed from Paris Saint-Germain and Ajax respectively, would play against Dortmund, Pochettino answered "maybe" in both cases.