Slow beginnings

Hey everyone.
I have a bit of a problem starting sessions of Monsterhearts. It's not that we don't have a lot of fun, because we definately do, but starting a new game seems slow.
I don't mean the initial setup, selecting skins, asking questions, creating the town and such, that's quick and greatly enjoyable.
I'm talking about what happens after that.
How do I, as GM, start out sprinting? I mean, I have a threat planned (loosely), but I tend to start the group in the classroom and then... I freeze. I simply have no good way of getting the ball rolling.
I think maybe I'm scared of starting out too strong and scaring people off.
What I'd really like to know is: How do you guys do it? How do you start out?

I always create a seating chart, but I don't always frame a scene taking place in the classroom.

The way I've been doing one-shot setup is:

Put 10 Skins on display (omit The Chosen, The Serpentine, a couple others).
Have everyone take 2 Skins and read their italicized text aloud.
Have everyone pick a Skin and fill out the front.
Ask them to state their look, ask 2-3 leading questions for each.
Write the seating chart.
Explain dice + stats + moves + Strings.
Have everyone complete the inside of their Skins.
While they do that, figure out what the first scene is going to be.
Go around the table and ask everyone a question about the community.
Frame the first scene.

The setup prior to the first scene usually takes 1 hour on the nose.

I set the first scene in the classroom if it seems like there's going to be drama. If not, I root around for another option for a first scene (big game? Rumble in the parking lot?). If I'm really stuck, I'll pick a starting relationship as defined in Backstories and frame hard into it: "So Jacoba, Levi's been following you around for weeks, sniffing you and going through your stuff. It's gotten weird. When and how do you confront him about it?"

Thanks for the reply, Joe.
I think I may have been a bit unclear, though. Our setup goes swimmingly, fast and fun. We enjoy setting up social disasters. Allison is always dead (I loved the "What's eating Allison" writeup, so as an homage we always start with an empty seat where Allison used to sit).
My problem really is framing the first scene. Possibly the last one as well, but we're only three sessions into the longest running of my three Monsterhearts campaigns.

I'd love to start with a BANG!!! I think I may just be too cautious and wanting to feel out my players a bit. This is strange to me, bgecause I run a helluva lot of games for strangers at Fastaval written by someone else, and there I have no problem throwing people into the deep end of the emotional pool.

Maybe the problem is that I don't really have the characters' personalities down yet, I can't yet feel what might affect them. Also, we establish their backstories such as family, after school job and such, in play.

All that being said, it's amazing after the first hour or two of actual play as we get a feel for oneanother. I just want to wow them from the word "Go!".

Yeah, I had trouble with the start too.

Set-up was great, and then I had to come up with the first scenes. And ... nothing. Totally blocked. I went with "follow them through an ordinary day" and had two pretty boring scenes. But then it started and conflict was found and it all sped up into a fantastic session.

I experienced the same with The Mountainwitch and I wonder if this slow start is actually necessary to develop a comfort with character and setting to build the scene for the later play. Dunno.

Joe gave good advice here though and I might benefit next time I start a new MH campaign.

I don't have much to add. As I've never MC'd a game I can only go from what my MC did. And that was to start off with the classroom scene and before we had fully settled into our characters totally. He sprung a 5 minute oral history report on us that we'd forgotten about. All the while that we were giving our report and scrambling the popular kids in class were texting about us on the sly and making fun of us. It worked well to immediately make us feel like the outsiders and give us a focus for drama/aggression. And to make adults/teachers seem completely useless and blind to our troubles.

Something I've tried out with some success is to play out the backstories as mini-scenes or vignettes. It's one thing for the infernal player to say "Oh, yeah, the Chosen thinks they can save me. I'll take a string on them" and another for them to narrate a scene where the Chosen has actually saved their ass from a whooping and yet you still end up with the emotional leverage from the scene. It all adds detail and colour to the setting that can then be built on.

After that, the PCs should have started working out their agendas, so you can put it to them as to how they're going to pursue them.