The Aviva Premiership leaders take on a star-studded Toulon side at Twickenham on Sunday in the semi-finals of the competition.
Last year, Sarries crumbled at the hands of Clermont Auvergne in the quarter-finals which Spencer feels has helped them improve this season.
"When we look back at last year we were good through in the group stages and then came up against Clermont in the last eight in front of a big crowd at Vicarage Road but we came unstuck," Spencer told Sky Sports News.
"The club and players have learned from this. It is a difficult step up, so it is a big week as we know we will have to put the work in and train twice as hard.
"The Heineken Cup is a really special time around the club. Everyone knows it is a completely different standard from the Premiership. The very top teams from around Europe are involved so we know we've got to raise our own standards."
Spencer has made 27 appearances since joining from Cambridge in 2011.