Set up two of the same Paradigms, and have them close to each other in
the top of the menu. You do not have to use the same ones, but do so if
it is the best attack. You might want to try this with your battle speed
set to slow until you get used to the process. During turn 1, let your
ATB charge. For example, if you have four attacks, during the third
attack display the "Paradigm" menu, and highlight the next Paradigm.
Once you see your fourth attack on screen or guess the timing for turn
2, use the extra ATB. After using this extra ATB during turn 3, charge
your ATB so you can use it again. You must charge a turn to get an extra
ATB. However, you cannot use an extra ATB to get another extra one.
*Note:* You can just charge the ATB half way to get an extra one. For
example:

Turn 1: Attack, then switch Paradigm at end of attack.
Turn 2: Extra ATB attacks.
Turn 3: Repeat turn 1.