Part Three of Ferrex's trilogy on Forge is up at Bungie.net: Advanced Forge Editing. It covers how to edit objects in ways specific to creating certain goal-oriented gametypes, instead of just piles of fusion cores.

Not that there's anything wrong with that.

What this article does talk about a lot is spawning: spawn points and spawn zones. If you've always been interested in how Halo chooses to spawn you where it does, this article is a treasure trove.