I've noticed something in various recordings (and sometimes even broadcasts) of people reading stories aloud: readers sometimes tend to read REALLY DRAMATICALLY!!!!!!
It's like someone told them that they should do a dramatic reading, and they assumed that meant they needed to overemphasize certain words and even syllables! that wouldn't normally be emphasized! To make it more dramatic! Sometimes even whole sentences! . . . And sometimes there are too-long pauses for no clear reason.
I suppose it's really two problems: one is overemphasizing things, the other is emphasizing the wrong things. The former problem, I think, often derives from wanting to be dramatic rather than boring; this approach also often involves imbuing the intonation of quite ordinary phrases with too much emotion. The latter problem often derives from the reader not actually understanding the meaning of what they're reading. (I've seen this happen occasionally in Shakespeare performances as well.)
Of course, readers can also underemphasize things; I suspect some people read too dramatically because they've been told that people often slide into a boring monotone when reading. In my experience, though, not too many people get monotonic when reading aloud.
Anyway, my real point is that most of the time, it works well to read aloud in a natural tone of voice, saying each sentence the way you would speak it in conversation. Not true in all cases, of course, but a good general rule of thumb.
While I'm on the topic, I suppose I could mention a couple other tips for reading aloud well. I was going to do a bullet-item list, but then discovered that I'd already said most of what I wanted to say in my guide to story reading. For example:
I highly recommend reading the story to yourself at least once out loud before [reading it aloud to others]. This will help alleviate such embarrassing problems as suddenly discovering that you have no idea how to pronounce a word that you've known all your life. [. . .] Rehearsing the story has a couple of extra advantages: first, you can find out how long the story will take to read (the two-minutes-per-page rule is only approximate); and second, you can work out how to say things. Long, convoluted sentences with odd structures are often hard to say with proper emphasis; think about how you'll stress words.
I guess that brings up a more general point: I think a lot of people think that because they know how to talk and they know how to read silently, there can't be anything hard about reading aloud. I would urge such people to think of reading aloud as a performance (while bearing in mind that performances don't have to be overdramatic). And as with any performance, a little bit of rehearsal can result in a much better experience for the audience, and much greater appreciation of the reader.