Answer: The trick is to hint at what will happen, without giving everything away. Because the hint will make them anticipate, and want to know more, Maia. I'm going to copy a handout that I used to use in my classes, that explains how to use that technique, which is usually called "foreshadowing." I'm surprised your editor friend didn't use that term.
Good to hear from you, Maia. Always good to hear from former Writer's Digest students.
FORESHADOWING, TENSION, & SUSPENSE
The transition establishes where, who and when, and the hook leaves a question which must be answered. I'll use an example from my own work, so as not to embarrass anyone else. The initial hook can, and should, foreshadow (hint at) the first crisis. For example, the first transition in my novel GHOST DANCER, goes like this:
Fort Benton, Montana
"GHOST DANCERS?" Christianna Lawrence jumped as Jim Hill's rich voice boomed clearly through the closed door of the colonel's inner office. "Don't be an idiot, man! You can't think some religious tomfoolery amongst the Indians will be any problem to my railroad crew. The Indian wars were finished years ago!"
In the above transition, the "hook" is the possibility that the Ghost Dance cult may cause trouble during the railroad construction. It then follows that the first crisis should be a manifestation of that trouble and sure enough saboteurs attack the train and leave Indian sign behind. The foreshadowing is a hint -- no more. It doesn't tell everything that will happen, but it promises the reader action that will involve an "Indian War." That way, when the attack comes, the reader is fulfilled, because he anticipated it.
FORESHADOWING is a technique that leads the reader smoothly along, hinting at what is coming next without giving too much away. Foreshadowing makes future action more believable. Most of us don't notice it, but when it's not there, crises seem too precipitate, changes too sudden, surprises too surprising. Properly done, foreshadowing will increase both TENSION and SUSPENSE.
The term tension, in fiction writing, has to do with the amount of stake the reader has in your characters. The more the reader cares what happens to your protagonist, the more tension there is. Hooks increase tension. Editors have said (to me) that a manuscript with middle sag "lacks tension." If the first crisis is resolved and we're building toward the second crisis, but nothing much is going on, tension can be increased by inserting a scene that magnifies the danger to the hero or heroine. And any scene that makes it look like the protagonist is in danger of losing what he or she wants can increase tension. If the danger is a psychopath, show him hiding behind a bush plotting the protagonist's demise.
To a fiction writer suspense is keeping readers guessing what will happen next. The term suspense, denotes how involved the reader is in your plot. If he or she already knows what is going to happen, there isn't any suspense (critics call it "predictable"), and little reason to continue reading. To avoid trite plots, make a list of 10 things that might happen next and pick the least likely. Or brainstorm with friends to come up with suggestions for unusual and exciting twists. Remember, keep the readers guessing and let the answer be a SURPRISE.
Foreshadowing is vital if the following action will be hard to swallow for some reason. If you're going to "Raise the Titanic" on page 367, you have to foreshadow the action in the first third of the book. Clive Cussler put in a scene where someone had invented a new underwater sealant and the hero used it to successfully raise barges off an oil rig early in his book. That action took place BEFORE any of the events that made raising the Titanic a plot necessity. Even though we all know the big T is still down there, foreshadowing made the reader believe it was possible, and Cussler made us SEE the action when she rose.
One way to convince a reader improbable action is possible, is to juxtapose it with everyday things. Barbara Michaels always has her characters discuss their ghosts, satanic-possessions, and hauntings while eating hamburgers or pizza. The reader believes in the hamburgers and "swallows" the ghosts too.
Another technique that will help readers believe in the impossible is denial. The more other characters, especially the least liked ones, tell the protagonist he can't succeed at whatever impossible task he's aiming at, the more convinced the reader becomes the hero can actually pull it off. Remember, the reader is, or should be, on the hero or heroine's side.