When I first started with maya I had this problem a few times too. Acctuall, I still have it sometimes. It helps if you make sure you allways have a second back-up file of the unsmoothed model. It does the trick for me.

You could also try to give the model soft edges iso smoothing it before it is finished (edit polygons - normals - soften/harden - [] )
Select your model, and the press the button 'all soft'. If you render the scene now the model looks pretty smooth. But in some cases this command just doesn't do the trick.