Start by having them roll intiative.
Seriously, start in media res, and then color the scene afterwards, and go from there. Why are they in that fight? What are they doing there? Etc. That should leave them with enough to experiment with.
That might not give you something to work with as far as an adventure. So here is a real suggestion:
Do the Ye Olde "You all have recently been looking for work, and so have been contacted by an individual who needs a job done". Cue a shadowy warehouse. The PCs are assembled, and asked to do a simple job: disrupt a party. More specifically, a business deal between a Bandit Lord and (insert gnome anarchists/any other magically potent type). All the PCs are tasked with is making sure the deal doesn't go down.
Sure, it comes straight from "Three Days to Kill", a module, but I think it's a nice fun way to start on a different foot.
Option two: Watch "Night of the Living Dead". Repeat it. Necromancers need not apply; just the dead walking, laying siege to small town in the middle of no where, and the PCs are trapped and need to survive. Though if you want to change it up a little, toss in a few different undead types.
Any other suggestions will require details about your PCs, their backgrounds, and the players' tastes, to detail it to your party specifically.