I like to relate Mini Empires servers to the Total War games series. If you're familiar with the Total War series then you're pretty much ready to go, if not it's pretty much like a Real Time Strategy game. You have to build your kingdom/empire and either outlast all the other empires or dominate them, of course you'll have to ally and trade with other empires in order to survive, because you can't simply conquer your way to victory without getting ganged.
Most of the common era's are Medieval, Modern, and Space mostly cause their the 3 basis's for roleplays. The reason I call them basis's is because there are servers that generally take the idea of lets say Modern and instead of being all "lol i blow you up with my nukes and my apache helicupters", they go back to the 20th century. I've seen multiple World War 2 based servers along with some World War 1 based.
My favorite basis era will have to be Medieval, it's simple and easy to follow and build imo, I'd suggest you begin there. Space/Modern mini empires are somewhat tricky to build around troop-wise, and most of them have multiple worlds and it's just somewhat confusing to me.
If you're going to start in Medieval and you aren't sure how to start of, base your empire off of another. I'd suggest for starters just go with the Roman Empire because it's somewhat simple, although I don't really base my empires off them a lot. Depending on the map you'll want to start in areas with grass if there are different biomes within the playable map.
There are some basics for a medieval empire, such as a Barracks, Mines, Watchtowers, a Governors Palace, Residential Areas, and Farmland. You additionally should add some Stables, a Trading Post, Protective Walls, and possibly a different district for your Military.
When invading a enemy you'll want to establish multiple camps and forts as you push the enemy lines, and always have a ally either with you or on standby. Also, take some of the more larger cities the enemy holds as you make your way to their capital and have some sort of navy to blockade their ports. I'd have some sort of unit type that'll most likely disrupt enemy formations such as Warhounds and I'd always have generals with your larger armies to keep morale up.
When you know you're going to be invaded, invest in some sort of artillery such as Trebuchets or Catapults, and send out some spearmen and archers to wait for the enemy forces. You'll really want to have a ally with you or waiting to flank/ambush the enemies coming to invade you because they'll probably have allies with them or a much larger army than yours. Also, I'd also still have a unit type that'll disrupt enemy formations here, depending on where you are I'd go with Warhounds, but if you're really desperate or you just cant get your hands on warhounds, elephants, that is if you can even obtain elephants as well. Also, have naval troops to defend your coastline/ports.
I'm somewhat too lazy to keep on going so I'll just leave you with that.
