Don’t play it on tactician, but the difficulty one down from that. The game is not uber hard, but you’ll die a fair bit in combat. A lot of the time this will be down to positioning and strategy rather than being underpowered, so persevere.
Specialise with your characters. There’s no point in having a team of well rounded jacks of all trades. You want people with specific strengths.
Use archers and always get the high ground, they become super powerful about halfway through.
Always strip away physical armour and use attacks that knock enemies down. If you can keep their biggest hitters down then that’s half the battle.
Also speak to and do everything, it’s great to experiment and the narration is hella funny so there’s always something to find