So you've got these characters, and each of them want something. Lots of different "somethings" actually and several of them are contradictory.
Within your story, these characters are busy doing this and that, these actions often related to their desires, but not always.
Meanwhile, the characters don't live in a vacuum. There's a whole world out there. Furthermore, that world can be separated into sub-worlds: natural worlds, social worlds, mechanical worlds, etc. Those worlds―usually indifferent to the desires of the characters―nevertheless impact the characters.
You almost have to ask: how's it all going to turn out?
Your readers will certainly ask that question, and you have to come up with some answers.
Every sentence you write poses questions.
"Sue strode into the store." Why? Will she find what she wants? Will she be able to buy it?
"Robin proposed dinner." Will the other person accept? How will Robin respond? Will the suggestion prove a mistake?
"Andrew turned the knob." Will the door open? What's on the other side? Is Andrew in danger?
Most of the time, questions posed are answered in short order. When those answers are delayed, that delay produces suspense.
Sue strides into the store. Will she get what she wants? For that matter, what does she want? Why does she want it? How will attaining it change things?
Questions produce suspense.
Confound your reader's desire for answers.
"Sue, is that you?" He backed her against the door, continuing to talk as though he knew her. Barry, that's who he was, that annoying guy who caused her to quit her first job.
More questions. More importantly, a delay in gratification. All these words later, the reader still doesn't know why Sue strode into the store.
Eventually, however, the reader wants an answer. Wants answers to every question posed.
The longer the delay between question and answer, the more the suspense is heightened, and the weightier the answer.
If Andrew turns the knob and enters the room, the reader does not attach import to the fact that the door was unlocked. If Andrew turns the knob, wondering if the door is unlocked, stopping to listen, licking his dry lips, the fact that the door then opens seems more important. (Throwaway answers are a great place to hide details that will only later prove to be significant.)
Within the conventions of the type of story you're writing, try to vary your answers.
Yes, the store carries what Sue wants. No, she's surprised to discover there's not as much money in her purse as she thought there was. Yes, the store takes credit cards. No, the card isn't accepted, and the clerk won't return it, but reaches for the phone.
Answers that raise questions. Answers that raise the stakes. Complicate your answers.
Robin proposes dinner. The other person accepts, but proposes a restaurant Robin can't afford. The other person accepts, but Robin immediately regrets having asked. The other person accepts, but Robin throws up during the main course. Yes, but.
Andrew enters the room. Is he in danger? No, but the item he saw there yesterday is gone. No, but the door swung locked behind him. No, but now he doesn't know what to do next. No, but.
The biggest question should be answered last since the emotional payoff of removing that suspense will be lessened if the story continues.
The exception is the question of romance. For example, in many mysteries, only after the crime is resolved does the story end with the answer to whether the two characters will intensify their relationship.