Well, first - This tutorial will teach you how to make a VERY quick, but pro terragen render. - The first time you use this tutorial might take 5-10 minutes, but after that you can literally generate landscapes in 30 seconds max.
Well lets get started.
I'm assuming you already have terragen v0.94 (the version must be 0.9 or similar). If you do not, you can download terragen here.
Once you've opened terragen, download this Terragen Pack (click) - You must download the terragen pack, or you won't get a result even close to mine.
Now extract the terragen.zip folder and leave it. We'll be using the files in this folder later.
Open Terragen and click "View>Landscape". (at the top) Click "Generate Terrain" and use these settings:
Click "Close" now. Now, you should see "Surface Map" near the bottom of the Landscape Window. Click "Open". Then open your terragen folder you downloaded and extracted earlier, select the "Surface Map - Green" file.
Now go to View>Atmosphere and click "Open". Find your terragen folder that you extracted earlier and select "Atmosphere - Yellow-Blue". Now close this window.
Now, on the rendering control window move the detail bar all the way to the right. Now click "Render Preview". If you like what you see click "Render Image" and save it.
Here is my result: