I'm lucky inasmuch as my regular writing partner is a trained actor, so each time we sit down to work he typically reads back to me what we wrote last time, and right away I can hear if something sounds awkward. He's also good at pointing out when things are grammatically correct but tough on the ear or difficult to say.
I also love table reads. Last year I had a bunch of actors go through a script several times, but we'd switch who was reading what role each time, so I got to hear a bunch of different takes on the same characters. One actor improvised something for a character that was so funny that it changed the way we write that character now.