Longer, more complex sentences are much smoother and more graceful on the page than in the mouth. If you want dialogue to sound real, listen to it–literally. Reading silently, your brain fills in and evens out. So, when you feel your work is in pretty good shape, read it aloud. Any place you stumble needs to be reworked. Reading your work aloud–whether prose or poetry–helps identify rough patches, awkward words, and other problems. If feasible, it’s even to have someone else read your work aloud for you.  Good listening!