An offensive paradigm like Relentless Assault allows you to concentrate the party's attacks on a single enemy and quickly stagger it. Stop those attacks, and the chain bonus you worked so hard to build will begin to fall. As a result, it may seem like a good idea to stick with Relentless Assault for the entire battle.
However, some enemy's powerful attacks are capable of reducing your party's HP to dangerous levels. If any of your party members take too much damage, shift to a paradigm like Solidarity that contains a Medic and heal your characters before they're knocked out. Avoid using a defensive paradigm for too long, though. The longer you use it, the lower your chain bonus will fall and the harder it will be to stagger your opponent.
Pay close attention to both your party's HP and the enemy's chain gauge, shifting paradigms as needed. In the early stages of the game, your best bet is a paradigm composed of Commandos and Ravagers like Relentless Assault. Focus on driving up the chain bonus until your party has taken significant damage, then shift to Solidarity to recover. As soon as everyone has been healed, switch back to offense. The goal is to stagger an enemy as quickly as possible, so do your shifting efficiently, without giving its chain gauge a chance to recover.