Originally posted by GunsForBucks:

You also want to clear the area of smaller trees and brush. Enemies will not spawn in line of sight. So clearing things that block vision will prevent them spawning as well.

I have to concur with Blank. I have a HUGE mud beach i've created for the purpose of beaching serpents. I've cleared an area about as large as two football fields, completely removing trees and stones and leveling it to sea level. Its mostly meadows with a patch of Black forest. The spawns happen right before my eyes, necks, boars and greydwarfs. At night the Gobbies come (its ok though because I have about 50 2 star wolves on the beach).