Summary:
Welcome to your new home. After finishing your Military and Defense Trees, this is where you're going next. While very expensive in terms of Time, Gold, and Research Stones, here is where you're going to get that next bump in your Troop Stats.
Essential Techs
Range Troop HP, Mail Armor and Accuracy:
Focus these if you are wanting to get into PvP as Archers will most likely be your first March.
Ground Troop HP, Plate Armor, and Zeal:
You'll want to max these out probably after archers unless you are going Ground first.
Mounted Troop HP, Armor Enhancement, and Fearless:
If you're just chilling, hitting bosses, and not doing much PvP; you'll want these first. If you're doing PvP, these are going to be last as you're not likely to see full Ground Marches until almost 6m-year into the server.
Siege Machine Structure, Heavy Machine, Collision:
Once you've hit K33 and can start focusing Siege a bit more for your defense, you can start bumping these up along with the others.
Raid:
Nothing wrong with a faster march speed to get you where you're going
Help-Seeking and Adv Help-Seeking:
Bump up your Embassy Capacity so you can take more reinforcements.
Prestige and Adv Prestige:
More troops means more killing!
Rally Horn and Adv Rally Horn:
Bigger rallies hit harder, no reason to skip this if you're the Rally Setter for your alliance.
Legion Expansion:
The long awaited graduation into the Big Leagues. Lock in the 6th march and never miss a rally again!
All the Debuffs:
Just get them all!
Non-Essential Techs
Conscription, Conscription Expansion, and all the Training Techs:
Nothing wrong with making troops in small batches. Might as well focus your time elsewhere for now.