Crowd Control and High Ground is a must, examining Mobs to learn their Resistances or weaknesses helps too.
This. The key is to learn the weaknesses of the enemies and play off of elevations/height advantages. Playing in a group that plays off one another is also very important. Your team should check your weaknesses and you should check your team's weaknesses.
Having 1 range, 1 mid, 1 cc 1 support is the default solid build. I have seen builds that are hyper-offensive with 2 range and 2 cc, but they don't do well if they get caught off guard. Same goes for builds that are too fragile with 2 range 2 support/3 range 1 support. Team building is another layer of complexity outside of character creation.
It all comes into play when you realize how many possibilities there are during combat. I.E: (said this earlier) I play Metamorph Red Prince who defaults to Dragon Breath and have my buddy playing Aerotheurge Sebille on standby to put out my fires with rain to create steam that my other buddy playing Rogue Fane can hide in when he bounces into the steam for an attack and then back out for Sebille to electrocute when the ground gets wet the following turn, leaving any survivors for me to pick off with Bull Horn Rush.
Later on, getting skills like Flight or Teleport really allow you to take advantage of the map, forcing you to analyze the terrain style, the layout, the height, the distance, and the resistances of your enemies. Tougher foes will have resistances to everything/armors/shields for everything, so getting Pierce abilities or Armor burn/steal abilities will help a ton.
This game is fucking amazing.