There are a lot of map sites where if you have enough gold, you can buy a unit/spell/artifact and avoid a fight. To get gold you need to enslave by beating up the residents of farms etc. You can choose to get increased gold and notoriety per turn. It's also a good idea in the early game to try and visit as many low notoriety sites when you are still at low notoriety, medium sites when you are medium notoriety etc. Also, while some sites that CAN have a non-combat option sometimes don't (so you still need to be ready for a fight), you need to play the game a bit to see how the different map sites work. I'll tell you one map site that never produces combat, and you can get a new spell for 3 random mana or 25 gold - the Mad Hermit Hut. Note if you have higher notoriety than the site you're visiting, the enemy gets reinforcements, but ONLY if you have a fight. If you are able to choose a non-combat option it doesn't matter what your notoriety is compared to the site. But different kinds of town/city settlements don't always give you a non-combat option, so you need to prepare for that.
And then again, the way you play depends on leveraging the abilities of your archetype (class). For example, the starting one is a Lich, who gets some good starting spells, and can sacrifice 5 souls on the strategic map to get 5 health back. He also has a Magic Dart that gives you mana if it kills a unit.
Note you can currently cast strategic spells when a screen is up but you're not in battle. Probably the only ones this should be banned for are the ones where you take immediate damage, as you don't get the damage until the battle screen pops up but it would be illogical to, say cast a healing spell when the damage you've already taken would have put you down to 0 HP or below.
I'll let you explore the other classes when you get to them. 
The game has simple mechanics, but it requires a great deal of skill to win. I won my first game yesterday, after probably hundreds of play-throughs.
