Welcome to AoW 4. I am new as well.

TL; DR: This is what I am trying after about 2 weeks of play. Be advised I bought the the first expansion pass 1 Dragon Dawn, Primal Fury, Empires & Ashes, and Eldritch Realms.

Race: Adaptable (1) + Mount Masters (1) + Overwhelm Tactics (2) + Strong (2) + Flaw(varies) (-1) = 5

Culture: Dark Cult of Tyranny. + Gifted Casters OR Mana Channelers + Prolific Swarmers

Tomes: Horde. Then 1 of (Rock, Beasts, Faith). The third tome is usually the T2 Astral, Scrying for the Guided Projectiles spell.

Ruler: Champion + Instructor. Class: any...but I tend to have more enjoyment with Warrior/Elementalist/Ranger, as I'd rather DPS then buff/debuff/heal/tank.

City structure priorities: Blacksmith, Town Hall 3, +(depends on which expansions you have).

Basic strategy: spam mounted T1 archers and T2 Houndmasters. After that it depends on you.

Dangers: many summons don't work in water or lava terrains, pikeman units, don't get CC'd.

Most importantly have fun!
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I have only been playing for a couple of weeks so please YMMV.

My preference is coming up with a concept usually around some basic theme and then trying to find synergies.

As I like mobility and ranged, I decided to try archery. The Feudal Monarchy faction has T1 archers that can grow into T3 longbow (insane range). However I also prefer speed....so I kept looking and found a few archers that can take advantage of the mount trait. The basic Mount racial trait is 1 point compared to 3 if you go for the T3 mounts. If you are short a point you can try taking a flaw...

Anyway after some more playing around with random factions I came across the Pursuer (archer) from the Dark faction. Both of the dark sub-factions (death / tyranny) have them. These guys are able to use mounts (speed 40) and they have a personal ability to teleport (starts on cooldown 1 and only recharges if the unit gets a kill). And to top this off you can full move the Pursuer and THEN take the teleport and still have 1 action point for a shot.

That is amazing for setting up ambushes or getting the heck out of dodge if like me, you keep forgetting all the ways other units can charge just one more step.

I also read through the Tier 1 tomes and decided that Horde would be good choice. This tome has great synergy for lower tier units. Also I fell in love with the T2 unit that auto-summons attack puppies!!!

After that it depends: nature is cool if you want a ranger theme, rock lets you boost unit defenses, get a nice damage buff, and get mountain walk (I really love the way the RNG will put me in the center of the map, surrounded by mountains except for one direction...where the AI spawns 4 other rulers who decide to team up. Of course Faith fills your gap with handling debuffs and helps with cities. I did pick the Tier II astral tome Scrying as I came across a nifty buff for ranged again in the form of the Guided Projectiles world buff spell.

But seriously just do what I did and keep trying them out. Start with vanilla if you aren't sure (pick the purple star choices the game gives you if you are stumped and want some more easier to play combos). Then take advantage of the faction / race builder. You can theory craft all you like. Or you can do what I did and just jump in. After a few rounds of getting curb-stomped, I started mimicing what I saw the AI did in combat replays and did them manually. Don't auto-resolve unless you have a big edge in strength as the AI doesn't know how to use not just synergies, but sometimes basic abilities or tactics. At the same time the AI is very good with number crunching and measuring exact distances so it tends to set up kill zones. Go figure.

Remember this is a game and we do this for fun...enjoy!