If you have enchanters, then anything with 2+ essence is a great fortress to train units in.
If not, you want a 3 essence fortress if you can get one. 4+ grain should always be a town - and a conclave can be any irrelevant city with at least 1 mana (so you can cast meditation). Enchanters is very very nice, and it can turn a piece of crap starting point into something nice.
So when you have to choose between "2 average cities" and "one great city", ask if the "great city" has 5f/3e or 4m/3e. Either way the "great city is better", and it is better to have your great city be a fortress than anything else.
Food determines a LOT, so i can not stress enough the purpose of the town.
Normally, i like to get one fortress with 3 essence, 2-3 conclaves with 1-2 essence, and 5 cities (all 5 become guild grocers!) and all enclaves become the thing that produces +1 crystal unless you really need the extra mana.
So how do you settle the world? Well, you have to start by getting your sov/champ a few goodie huts and weak quests. If you get the archer unit quest reward and a token of the sand golem, your in great shape! If you look at the later game spells, one of them changes worthless dead land into vitalized land. I believe the tiles become dead because the total yield of the tile does not equal 6-8 +/-1, but i could be wrong.
Kill the weak monsters, start any quest that is safe to start (once you start a quest, the AI can't steal it) and start looking for victory conditions. Nearby wildland? thats as good as a weak neighbor, but some of those wildlands have ridiculous units that you won't be able to kill - until you get used to using world map spells to deal your opponents damage and debuffs pre-battle.
I used to suck really bad at this game but learning how to use magic well; i usually research "green only" after henchmen, and research the extra food tech 5-8 times before doing blue-red techs. Why do i do this? Because with world map spells on your side, you can't lose!
So have fun, get to know the mechanics and spell synchronicities. I gave you fire/earth and death/water - there is also air/earth and i think water/air (i could be wrong on this one). Once you understand what abilities the spell levels really give you access to, your first turn will look like this:
Settle good spot.
cast meditation in capital/set tech to civics, cast tutelage on sov, tutelage on champ, and your good to go. If you like a beat 'em up, i suggest you learn grow-shrink, and haste-slow. Otherwise, if you like magic as much as i do, you will rarely see an enemy actually make it up to attack your Sovereign.