If you're having trouble, one thing I recommend is using less units. The first few playthroughs I did, I tried to keep everyone fairly balanced level wise, and that made it harder. If you instead focus on eight to ten characters and ignore the rest, you'll end up with a good team that won't have too much too worry about.
Another piece of advice to make things more manageable is to use Seth, he is far and away the best character in the game.
Another mistake I made was ignoring the weapon triangle in my first two playthroughs, I thought 15 hit rate, and 1 damage, no big deal.
It really is a big deal, the altered damage alone makes a regular difference, but the big thing is the 15 hit rate is the real big one.
If you try to keep the upper hand, you'll very rarely miss attacks, and you'll dodge significantly more.