When I first started out in voice over, I was under the very erroneous impression that I always had to sound "professional" and, you know, sort of flat. So I'd do a read for my coach, Nancy Wolfson, thinking I sounded amazing, and she'd basically yell at me: "Trevor! Choose a color! You need to choose a color - and you're clear, no color at all!"
I got it. I still hear her during my reads.
I've been reading Teri Apple's book, Voiceovers: Everything You Need to Know About How to Make Money With Your Voice, and she says the same thing: Choose an emotion.
When you're reading a script, don't just read, feel what you're saying. Read it first a few times, decide on an emotion and go with it. Don't worry about every little word - if you're feeling it - and just saying it naturally, you won't have to think about it.
Try it.
Trevor Jones Voice Over