Spawn Cycling:
-1st SI to die, IS in next hit.
-4th SI to die, is NOT in next hit.
-It is recommended Support Class (Boomer/Spitter)die last in order for next hit setup to not be a 2 and 2. (Smoker, Jockey, Boomer, Spitter)
-If you have both a Boomer and Spitter, depending on if the next hit will be in a Small Room or a Big Area, you should cycle accordingly.
-Small Room: Spitter (Trapped in spit damage) Cycle Boomer last.
-Big Area: Boomer (Horde damage from all sides) Cycle Spitter last.

*Note: All Spawns should generally attack at the same time and die within the same time in order for the proper Spawn Cycle to work.
*Also, this is very helpful for you to know so you can cycle for specific hits. (ie: Top of ladders, Deathcharge areas, etc)