Star Renegades

This is the first boss in the game
You can only face it with 3 characters
It has few attacks but does a lot of damage

I recommend facing it with a Tank, and two different DPS as for example:
Commando (Bentley) Role: Damage and Stagger
Spectre (Nava) Role: Damage and Stagger
Juggernaut (Aia) Role: Tank and Anti Armor

Aia can redirect attacks if they are single-target, on itself
Bentley has a better stagger than Nava but most of the time you'll have to use both of them to get a break
Nava has a lot of DPS compared to bentley, so judge by the situation when to attack

(There are many other compositions for the starting team but the gist of the speech is always the same, bring the boss to the break to avoid damage)

The boss fight must go something like this:

-Cause multiple break while removing the shield
-If you can no longer cause breaks and the boss is about to do an AOE, defend with all characters (or use a Stun, but each character can only do it once, evaluate well)
-Once the shield is removed, use your anti armor abilities, always causing multiple breaks and defending yourself when needed
-When the boss is naked, evaluate when to attack/break/defend
-The boss has a phase called Overwatch where he will counterattack you for every attack received, but it is not major damage
-You can be very aggressive as the whole party will be healed upon victory, even any dead members will be healed to the maximum

Remember that this strategy applies to practically all bosses, with a few small exceptions