Any tips or suggestions???
I recommend you read this first. It covers quite a bit, including spawning.
Invasion Conceptualization
Original post
The author is an avid invasion player and has much experience with the game. His article is essentially an analysis of how the bungie invasion games and maps are setup to play invasion effectively, and presents his analysis and conclusions as the bar that he looks for in any custom map that people present to him for comment. And his analysis is sound.
Additionally, you can learn about the mechanics of the spawn system at Forging Reach’s Invasion Spawn Tutorial. But the mechanics does not discuss effectiveness, which is what I think you are looking for.