I'm a bit uncertain of how to keep a scene with a lot of dialogue between two characters interesting. The dialogue is needed but I want to keep the story interesting but it's feeling a little slow. There's only so much you can do to describe things in a scene, only so many words you can use to describe they way voices sound and you can't overdo it. So does anyone have any tips on how to keep scenes with lots of dialogue interesting?

The dialogue itself, the actual words the characters are saying, need to be interesting. There's no way to dress it up (and like you said, going to far can be worse.) There may be a way to keep the scene interesting if it isn't naturally; what are the characters talking about that might be boring?

873708 If what the characters are talking about is interesting, then the dialogue will be interesting too, at least to some extent.

Of course, that's not enough.

Spice up the scene with some expressions and gestures. And, most importantly, remember to describe what your POV character is thinking throughout the conversation. Don't just write what the characters are saying to each other. Write the emotional fluctuations that your character is going through during the scene. If your character has the audience's sympathy, then they are going to be invested in what's going on in his/her head during the dialogue-heavy scenes.

873708
I concur with 873825, try to include the nonverbal communications as well such as facial expression, arm movements, pacing, etc. Just don't go overboard. Best advice I can give you is to read a real novel to get an idea as to how to do it.

I find just writing the dialogue with the way the characters are speaking at first usually helps, followed by cutting them out after a certain point. The reader can usually guess how the character is speaking or feeling during the conversation, so just having the text there and switching between the characters with different lines is a good way to do that. The readers have a voice for the character in their head, so setting up the back and forth rhythm is probably all you need to do.

873708 What I tend to do in my stories is have things going on in the background, just to break up large sections of dialogue (not all the time, just the odd interesting detail) For instance, I had a scene where Twilight and Applejack were taking shelter in the barn from a thunderstorm, and as they spoke the thunder in the background would occasionally interrupt them. I tend to use stuff like that 'cause it also sets the scene so it's a win-win.

Well, from personal experience I find that if a scene with dialogue gets boring I like to break it up a bit. Have one of them take a break from talking in which I re-evaluate the mood in the scene. Or I have somebody else come through and interrupt them, not knowing or not caring that there was another conversation going on, and then when they leave again the original characters in the scene can recommence their conversation. For example:

"The whole point was to have extras of everything." Twilight said dully for the umteenth time.
"But why would you need extras? It's not like you're going anywhere. Are you?" RainbowDash asked.
"No, Rainbow. I--" Twilight paused as the door opened and Mayor Mare walked in.
"Good morning. Isn't the weather beautiful?" The Mayor asked in a bright, almost sunny voice.
"Uh, Yeah. Amazing." Rainbow answered, not wanting to be rude but wishing the mayor would leave.
"Well I just came to grab my clipboard. wouldn't want to be caught in a meeting without it!" The mayor smiled, picked up her clipboard and went back the way she had come.
"I'm not going on a trip. I just don't want Spike to have to much running around to do." Twilight finished once the Mayor had disappeared behind the door.

Or I'll throw in a twist that will have a small, insignificant impact on the story to keep the reader's attention. So, for example, say Twilight and Rarity were having a conversation about how Twi's research and Rarity's designs are both ways of life, in which the girls are happy, but this conversation is to have an impact on the story, after a lot of dialogue I might do something like this:

"Your research takes absolute precedence over everything! Except of course us. I think we've all seen you drop your research to do little things for us." Rarity told Twilight, who proceeded to blush.
"Well, thanks Rarity. But I've seen you do the same thing with your dress-making. A lot more than I have with my research." Twilight answered.
"Thank you, Twilight. I suppose it does have some truth to it." Rarity smiled and proceeded to ask, "Would you tell me how Spike's been? I haven't seen him in ages!"
"Actually, he's not around. He's come down with the flu. It's pretty uncommon for dragons, you know." Twilight answered.
"Oh my poor Spikey-Wikey!" Rarity crooned. Twilight patted her back.

So there are two ways you can do it. Another way, though, is to add a lot of action in between lines. For example:

"Apple Bloom! Ah thought Ah told ya we only need the left side of the orchard done today! We need to keep this harvest organised 'else we'll never finish!" AppleJack was almost yelling, as she bared down on her little sister, who was cowering under the older pony.
"Ah'm sorry, AppleJack! Ah just got caught up in mah work and, well..." Apple Bloom slowly backed away from her sister and motioned to a couple of the trees she had bucked on the right side of the orchard.
"Ah understand, Apple Bloom. But ya need ta pay more attention!" AppleJack stomped her hoof to emphasize.
"Ah know. Ah'm sorry." Apple Bloom hung her head and turned to go inside.
"Granny Smith may need help making some pie if ya want." AppleJack told her sister, who looked up, smiled, and sprinted towards the house. AppleJack shook her head and laughed before following her sister.

And you could always just have the dialogue itself and word it so that it's interesting. For example;

"Spike you brought back the wrong ink!" Twilight moaned.
"No I didn't! You told me black!" Spike answered.
"And this is dark blue! Spike what were you thinking?!" Twilight was almost yelling now.
"Twilight wants the black." Spike answered. Twilight groaned.
"Then why didn't Twilight get the black, Spike?!"
"I don't know, Twilight! I asked for black!" and so on...

Other than that you could always try three lines of dialogue, a paragraph of action, three more of dialogue, a line of expression, three dialogue, one action, and so on... Example:

"Well, just don't get too comfortable. I'll only be out for ten minutes." Rainbow told Scootaloo, who had plopped onto her couch.
"Alright. You don't have to worry about me." Scootaloo answered.
"I hope not." Rainbow looked at the other two crusaders in turn and left.
The house was pandemonium as soon as Rainbow had fled the cloud. Scootaloo jumped off the couch and onto the kitchen table while Sweetie Belle and Apple Boom entertained themselves with a much nicer shower than either of their sisters'.
"Wow! Rainbow's got it good!" Sweetie Belle called to Scootaloo after feeling how warm the water got.
"I know! I kind of feel bad that we're going to ruin her house just to try and get our cutie marks." Scootaloo said, joining the others. There was a moment of silence before they all laughed.
"Good one Scoot! Remind me to use that one on Rarity the next time we use her house!" Sweetie Belle said between gasps.
"Yeah Scoot! AppleJack too!" Apple Bloom added.
The three laughed for a while longer before splitting up to use Rainbow's precious objects to find their cutie marks.
**Also note for this one that it doesn't necessarily have to be three dialogue, one action, three dialogue, one expression. and so on. It can be in any order, as you can see how I changed the order a little above.

So there are a few ways to go about this. I didn't know what your characters were saying so I just put everything I know about this particular subject.
Hope it helped!