The strategy is not spreading cities like wildfire and hope for luck with monsters, in my opinion.
I do as follows (challenging, dense monsters):
1. Recruit nearby champ
2. Clear out area nearby starting city to avoid local resoruces being attacked
3. Find a place for your second city so that its influence will not overtake any huge monster lair. Keep focus on clearing out as much as possible.
4. By now someone big will often declare war on you. Get one or two cities from them and you are going
This does not describe all my games, but is a general template for me.
If you are near a hoarder spider or other lair that spawns, then you are ok if you have a city nearby (not an outpost). If the spawn eventually always attacks your cities, then this will help you level any champ/unit that you place there.
Ignys gives lots of exp. A lair spawing them is great.
Since many monsters will follow you, there is sometimes a possibility to lead them towards enemy areas.
If you produce a few units, have a sov and a camp, then it is not long until you can survive pretty nasty monsters.
My most important tip:
The enemy wildlands (green borders) can give insane amounts of exp. Enter, fight and withdraw to neutral land to heal and upgrade. I did this yesterday before going to war, and had level 7/8 normal units with my sov. That army took two cities with pretty heavy defense.