Godrays ARE hard to get.

Some methods that ought to help:

1. Godrays look better and show up more from a distance, with a wide angle camera lens (small focal length).

2. A dark scene helps (thick clouds, etc.)

3. You can get a bit more control by using one or more transparent primitive cylinders to punch holes clear through the clouds, where you want your Godrays to be (thanks to Mark of ImpWorks for that).

4. If you get "grain" (too few samples) in your rendered clouds, use the "Quality" slider in the Atmosphere editor "Sky, Fog and Haze" tab - which will increase render time, of course.

5. If I remember correctly, volumetric lighting helps.

There's been a lot of discussion on Godrays, so you might want to do a search here.  

If you need to learn more about volumetric lighting, I have a tutorial...

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