Help with Iron Bull please

One trick is to take Turn the Blade and Turn the Bolt from the Weapon and Shield tree to make Bull a little less squishy.

Even if you're rolling Bull as a 2-Hander (which he should be), those passives still will apply. It does however require you wasting 4 points and having two abilities you can't use (best to deactivate them in the tactics, so Bull doesn't try to use them anyway).

Other than that, "Guard on Hit" materials never hurts to try to apply to his weapons/armour to give him more defense.

Do remember though two of the same tier DON'T stack (no +5 and +5 to get +10). However different tiers DO stack (so +3 and +5 will grant +8). The downside with this is that you'll need to do a lot of farming to get those mats, which requires patience, time and some degree of luck.

Bull does have a problem with being a glass cannon unless you build him just so. Even then he needs a bit of micromanaging from time to time, as his AI doesn't know how to use him or his spec properly. I get around this by making sure I have a lot of regen potions handy, so he's able to heal over time (and heal others with the upgrade).

Despite that though, he's never going to be as good as Blackwall or Cass. By late game, those two are practically immortal and capable of killing everything while you nip off to make a sandwich. I barely even look at them during dragon battles, whereas I'm always having to pause to drop a potion to keep Bull on his feet.

Also regardless of build, the Hakkonites are pure evil... especially on Nightmare. Even with full guard, barrier and health, their archers were managing to shred through or one shot my party. Endless waves of Darkspawn in Descent was a cake-walk compared to JOH. If you're having trouble with the Hakkonites, don't worry, you're not the only one who has trouble dealing with them.