Assuming that what actually happens is dramatic enough - it's not just a series of little trips to the shops - then I wonder if what your friend is commenting on is what I'd think of as a lack of
intensity in the writing.
The ultimate intense writing is good poetry, where every line is like a tardis of sound and meanings. And it's perfectly possible to make your prose more like that, without changing plot or characters - although you may find that the fiercer search for the vivid, immediate, leaps-off-the-page word means a fiercer search to understand
exactly what you're trying to say... which might change things a bit.
Yes to the stronger verbs. Not necessarily yes to the short sentences, since a well-constructed long sentence can drive forward much more strongly than the stop-start-stop-start jerkiness of a series of short ones. I wonder if it's also a matter of making your characters' physical experience more vivid, both in their space, and in their own bodies: of making sure you're really showing/evoking, not slipping into telling/signalling what they're going through:
This might help:
http://emmadarwin.typepad.com/thisitchofwriting/showing-and-telling-the-basics.html
and as that piece touches on and links to, it might be a case of trying to exploiting the full range of psychic distance. Even a reasonably close psychic distance can make the story monotonous.
These two posts are related to this, and might also be helpful:
one about how to ramp up the romance in a boy-girl plot where the writer's been avoiding it:
http://emmadarwin.typepad.com/thisitchofwriting/2011/03/he-looked-up.html
and one whose work is "too understated and gentle":
http://emmadarwin.typepad.com/thisitchofwriting/2010/09/jerusha-cowless-agony-aunt-understated-and-gentle-just-is-my-voice.html
Emma
<Added>oops
Even a reasonably close psychic distance can make the story monotonous,
if it doesn't vary.