Isabella: gets all the best rings and amulets especially + 1 to all attributes. Defense is crucial for survival so go for high cunning, at level 10 & 11 take ‘experienced hands’ and ‘sea legs’ for huge bonuses to attack, damage, defense. Also romance her for +5% speed bonus + 5% to hawk. Obviously take Dual Weapons (not lacerate), Swashbuckler (not savvy, not across the bow), and blindside before any other talents. I usually take control of Isabella in the big fights, target enemies about to die (1 hit) , protect mages, gang up on elites.
Friendly fire: Easy to avoid, don’t use fire or ice (except winters grasp) on auto. And don’t use Fenris or Carver on auto.
CCC: essential for NM. Lightening tree is very powerful, chain reaction on stagger is deadly, use Aveline to stagger enemies (2 ways to do it). And always complete 2nd power on any talent or spell for maximum effective use of your stamina or mana.
Immunities: look them up on the forum. You’ll need to hold several staffs and swap out when needed. Remember the more powerful the staff or weapon, the more powerful are all your spells and talents.
Autopilot: Setting these up to work effectively is covered elsewhere (big topic) but here’s a useful tip rarely mentioned, some spells require a sustain before you can cast them but on auto this is not required, i.e. Merrill can cast ‘Wounds of the Past’ without having ‘Blood of the first’ active, and your healing mage can group heal and revive without having Panacea active (simplifies things a lot!!!).
General: Unless you’re boxed in, always hold a good way back after the enemies are triggered and stay back, ‘hold’ your team in place, select ‘all’ and move them all back. In that way you can see what’s coming and plan an effective response (which for me is often Aveline sent to engage, Isabella picks off any that get past and the mages lay down a blitzkrieg of lightening, fists and spirit.