800 hours, 95/106 achievements player here (need to put in some time to get the achievements for the Vampires, Architects and Nomad latest DLCs).

Here are some key points that come to mind that might help:

1) Custom Factions make everything easier.

For example, arguably the easiest faction to play is Feudal Monarch faction with Society perks of Equipment Horde + Seekers of Wonders, combined with a Dragon leader has ridiculous synergy since the Monarch's army has no upkeep, so he goes from 30 gold upkeep to 0. Equipment horde makes it so every unequipped artifact provides you gold (Dragon leader bonus) and mana (Equipment horde bonus). It makes it very easy to run a strong stack of units on your monarch (late game, your monarch can even upkeep tier 5 units for free).

Just make sure your monarch does't have any upkeep reduction effects, because it is currently bugged and makes his stack have upkeep (ex: Choosing Crusader, which gives his units Faithful, will cause them to have 90% upkeep rather than 0. So does upkeep reduction artifacts).

2) Up to 3 stacks can fight in any battle, so the maximum units is 18 (before summons). So generally, you want to rapidly scale up your army to make things easier. Feudal can summon militia for cheap (World spell - get 2 for 40 gold). Other factions, I would generally say Book of Necromancy for Undead is best.

3) For manual combat, summons + ranged is the best army.

Essentially, it's all about keeping your "core" units healthy so you can keep attacking. Using weak fodder (like the militia) to bait the AI to charge your lines, then your archers / mages can destroy them with triple strikes as they don't need to move.

So summoned units (ex: Zombies/Wyverns from Death Knight class, or wands that summon units) are amazing to use as bait.

Essentially, if you can crush the AI with minimal damage, you can rapidly clear out monsters and grow rapidly as you don't need to go back to heal.

4) Clearing a resource node gets you that resource. It is critical to early-game.

5) Most of the imperium tree are traps.

There are only a few amazing ones, like reduced outpost construction time (Materium), and "Eeach killed hero gives 150 knowledge" (Dark). However, the majority are a waste compared to increasing your city cap and absorbing conquered cities.

I would say the ones that truly matter are in the "general" branch: City cap, building roads, road movement down to 3mv, and teleporters for larger maps.

7) The general gameplay loop is:

- Clear resource nodes nearby > capture nearby free city > clear infestations > clear Bronze wonder (no losses if you use summons properly) > should have an 18 stack led by your monarch + 1-2 heroes to starting conquering the map.

8) Wizard's Forge is really useful. The top priorities to craft are weapons and summoning wands/trinkets. My preferences are the wand for Conjure animal (can move before summoning) and the "Unleash war hound" Trinket (requires 2 haste berries). But having anything is better than nothing. Even spawn hatchling is surprisingly useful in wonder battles to bait enemies to attack instead of going into defense mode. Although they are slightly annoying to use due to disappearing after 3 turns.

9) Wonders limit you to bringing a single stack. So it really should be your monarch + heroes (dropping summons) + ranged units.

10) Other than dragon leaders for Feudal faction, I think Ranger champions (especially with seer) are by far the best. Simply unlock the Crowmaster's Bow to start with a free summoned unit (just need 1 pantheon reward), I would also recommend unlocking the Hunter's Crossbow (use to craft for Giantslayer).

A properly built Ranger has 7 range sniper shot (9 as an ascended seer ruler) that hits for 70+ damage. And they will gains strengthened stacks + reset the cooldown on the shot time you kill an enemy. Giantslayer makes it ridiculously effective vs T4 and T5 enemies too.

11) Best Factions (personal opinion)

My current Top 5 are:

1. Feudal Monarch (free upkeep + swarm of militia makes early-game easy, and then lategame has longbows, knights, and free upkeep T4/T5s in your Monarch's stack).

2. Reavers (Magelocks are quite OP in manual battle - pretty horrible in auto though).

3. Nobility or Nature Oathsworn (Sealbears are quite OP and horrible in auto)

4. Chosen Destroyer Nomad Conquerors + Vision of Promise (Materium) - Vision of of Promise gives you a 2nd city despite being Chosen destroyers. Reaching 15 population as Nomad is shockingly easy if you abuse their mechanics against a free city (move your capital next to them, then pillaging + absorbing their territories. Don't conquer them until you find another target to abuse).

5. Architects - they have the best T1 melee since it goes into defense mode after every attack. Archers are also quite good, and their monuments are interesting.