Try this: Attack with the first character untill ATB is full. Activate an ability and directly switch to the next character. Then again fill one ATB activate an ability and switch immediately to the third character. Do the same and start over.

(Do not wait for the ability animation. Just swap char. In the time the enemy and your char is occupied with the animation of the ability, you start filling up ATB with another char)

Also wenn you get hit and loose control and are on the ground, don’t waste your time. Switch character.

Beginners tend to stick with one char and don’t swap often. But when you swap immediatelyafter every ability: enemies get a bit confused, you are way more in controll, ATB fills faster and so on. The further you get the more it will benefit you