Get Over ItToday's Tune:
If there's one thing I've learned from writing ALL THE WORDS, it's that things are inevitably going to get cut. Scenes that serve no purpose for the greater narrative, needless words, boring filler, etc. And it's not just the "bad" stuff that gets the axe -- I've had to cut many a scene that I've absolutely loved, but it didn't quite work.
Even with all that chopping, there's still a chance that some relatively bland scenes are going to make the cut. An unexciting-but-necessary conversation. A homework assignment that serves a purpose in a later scene. Going to class because your character is, you know, still in high school. Whatever.
Such scenes may be boring, but they're often important to make the plot move forward or transition scenes smoothly. Still, they aren't naturally tension-filled moments. So how do we inject more tension and raise reader interest without coming across as forced?
Here are a few methods.
Make your scenes serve double, or even triple, purposes. Layer on that conflict. If you need a conversation to happen to convey important information to your protagonist, make sure there's something else going on to bring up the interest level. Maybe your character is in a rush to get somewhere important when they're stopped and they're worrying about where they need to be while the conversation is going on. Or maybe they're nervous about the person they like seeing them talking to someone else. Maybe they're convinced they're about to get in trouble. The possibilities are endless. A caveat: be careful not to have too many balls in the air. You don't want the reader to become confused or for important information to get lost in the shuffle.
Make something happen. Boring scene? Have something interesting happen. If your protagonist is in the classroom, have someone pass them a cryptic note. Have the teacher slap the desk with a ruler. Someone gets sick and has to leave. Characters play a cool game on their graphing calculator. Something. Just make sure to keep it relevant to the scene. Don't go for something so distracting or significant that it ends up a loose plot thread instead of a tool for tension.
Keep low-tension scenes short and to the point. If you're going to have slow scenes, keep them quick. (Is that an oxymoron? Eh.) Don't drag your readers through paragraphs of lengthy prose when you can make the same point in a few sentences.
Unless the scenes are truly necessary for plot movement, setting, or mood, cut them. Back around to cutting again, but it's true. This goes for any and all unnecessary scenes -- if you can cut a scene without confusion or choppiness, do it. If there will be some confusion, but it can be remedied with some general tinkering, then cut and smooth.
Use slower scenes to incorporate some internalization. Remember, tension doesn't have to be big and loud. It can be as quiet as stress from a recent fight with a parent or friend. If you have the downtime, use it to give your character a moment to think things over. Character development is important, but as always, be wary of waxing on too long or edging into whiny territory.
Amp up the dialogue. Conversations between characters should really serve some sort of purpose. Although people make random small talk in real life, you don't want to incorporate that into your fiction unless you're doing it for a reason. You can express tension in word choice, tone, whether or not one party is keeping a secret, or an escalation in emotion.
If all else fails, remind the reader of the stakes. I'm not suggesting you haphazardly drop in a stilted reminder of your protagonist's goals, but if you really need to beef up a boring (but necessary) scene, try to find a way to bring those stakes to the forefront again.
In closing, I'd like to reiterate that you should absolutely, totally, completely, 100% make sure a scene is necessary to the overall plot/mood/setting of the story. If you determine that it is, but it's still tensionless, then find a way to crank it back up.