Well it depends, are you making a multiplayer map or a single player map? I would try not to use the default grass, and go for a nicer detailed grass. You can find that in most of the model packs. Also, i recommend putting a lot of trees, some plants/tall grass etc. Just try to give it an outside feeling if you know what i mean
You may also want to look at Cosmic Prophet's models, as he has a very good pack that has trees/cliffs/etc!
Hope this helps! Sorry if this didn't....
-Josh
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