This is part 4 of my series on scenes:
A sequel contains three elements:
Your scene ended with something happening, probably something bad. So, naturally, your characters have to react to that disaster. If your wizard fell into a pit white battling a fire demon (to use an example that's probably never actually been used in a book before--what? Oh.), your characters need to respond somehow. They could just stand there and watch him fall. It would be better for your story, though, if they actually did something.
A reaction should have two components, emotional and physical. Good writers have no problem, usually, coming up with a good physical reaction. That the characters have to do something is obvious. Great writers, however, recognize that the emotional reaction is just as important.
Remember, the action is the plot, but the characters' emotions are the story, the reason why we care about them and spend hours following their travails when we could be watching America's Got the Next Dancing Idol Chef Survivor.
So, when your wizard falls into the pit, your characters should try to save him if they can. If they can't, they need to save themselves from sharing his fate. They also need to react emotionally. Are they relieved to be rid of the meddling geezer? Are they distraught at losing their friend and companion? Are they frightened? Lost? Let the readers know. Remember, though, that you need to use your best show-don't-tell techniques when writing about emotion ("Never Name Emotions" by Julie Daines).
After the characters react to the disaster, it's time to regroup. Regroup involves recognizing that there's now another problem, or a new set of problems. The characters recognize that, sure, they made it out of the underground passage alive, but Things Have Just Gotten Worse. There's no wizard to entertain the party at night with fireworks, smoke rings, and interminable stories of the past. Oh yeah, and without his powers, the quest just became far more dangerous, for a specific set of reasons.
The dilemma has its own set of emotional and physical reactions. Don't short-change your reader by forgetting to react, but these reactions need to lead toward a decision, an OK-here's-what-we-do-now moment.
If multiple characters are reacting to the disaster, this is also a good place for conflict. Remember, each character has his own agenda and goals, and comes to the problem with his own perspective. This naturally creates conflict as they try to decide what to do next. That conflict might bleed into the next scene, or it might be resolved when the decision is made. Maybe the party agrees that the next thing to do is to keep on with the mission to destroy the magical talisman. But one character--maybe he's the neglected younger son of the kingdom's steward, say--thinks the talisman should be used to help defeat the Big Baddy. Maybe your main character wants to protect his friends and run off to finish the task alone. These plans create conflict and up the peril.
The decision leads into the next scene. With a new set of problems, an increased sense of peril, and heightened conflict, you are ready to start the pattern all over again. You have everything you need for another well-crafted scene.