Experience vs. Inexperience: This has already been pinpointed in initial comments by both respective head coaches. Todd McLellan's franchise has qualified for the playoffs eight straight years now, and is the only NHL team to reach the conference finals each of the last two seasons.
Meanwhile, Ken Hitchcock's franchise hasn't won a playoff series since 2002, and hasn't won a playoff game since April of 2004. The "recent experience" aspect could be a factor in terms of players knowing what to expect in a magnified compete level, and also in a 7-game series situation, where the ability to mentally overcome odds is key.
Compromising the St. Louis system: It's clear the Blues earned the second seed in the Western Conference with their defensive play. Not only slowing teams through the neutral zone, but also in front of their own blue paint. When the puck gets low in their d-zone, forwards collapse and help out the goaltender in "protecting the house". If the Sharks and Todd McLellan can successfuly strategize and execute a plan to counter this system, they will win the series. St. Louis does not show the goal scoring potential to keep up with San Jose -- should this series become an offensive shootout.
Knowing how to overcome: This has been a recent postseason theme for the Sharks: the ability to overcome. It's an outlook that should not be lost on players, coaches, and even fans of any playoff team. Face it -- no shift, period, or even game is going to completely go your way at this point of the campaign... opponents are just too good. So you have to take some push with your own shove. You have to learn to ride the turbulence of what is ultimately a safe flight. Not getting caught up in any one negative moment is a key for any team hoping to hoist the cup.
Forgive, but don't forget the past: Percentage wise, the Sharks were the best team in the Western Conference in the first half of the regular season, hence Todd McLellan's invitation to coach an all-star team. The second half was drastically different, including a run starting in February which saw San Jose go 4-11-3. Although the second season is a clean slate, don't think the Sharks come into this postseason relationship with no "baggage". However that can pose well for them, if they move forward with the chip on their shoulder... knowing the bad places they've been, and knowing they had the attributes to get out of it before.
Make the momentum mean something: The Sharks finished their season 10-4-1, playing meaningful opponents who were fighting for their own playoff lives. It was a positive way to end the season, with the players feeling good about the final stretch. Meanwhile the Blues won only four of their last 12, as Ken Hitchcock tinkered with lines in trying to find the chemistry that made St. Louis so successful all season. Striking early in the series, and playing the momentum card would be a great initial boost to San Jose.