Question
there is 3 areas in my yard that I can't get grass to grow.  We have seeded and laid sod there.  The thing I notice most about these areas, is that it stays very wet.  Is there anything I can do to help the growing process of the grass seed or sod?

Answer
Gra:

If you have replaced the grass/sod in those areas, then, there must be a problem to solve before it can grow.  Not knowing where you are and what type of grass you have is a small problem.

You mention the constant wetness.  I do not know the topography of your yard, its potential for springs and captured drainage, and the drainage relief patterns.  I would suspect that you will have to drain those areas or fill them to move moisture away.

If the source of the water is a spring, then filling will only move it outward and upward or elsewhere in the yard.  If water is simply captured in these locations, filling will alleviate the problem.

If they are near some plant beds, you may consider incorporating them into the beds.

Other potential issues may be shade, soil type, fungus (brought on by moisture).  Once the drainage issue is solved, you can deal with these if results are not up to your expectations.

Best wishes.