Once you get good at using a specific character and increase their stats with better armor/weapons, play their story mode and Ascending Tower of Souls. The first few levels of each will be easy and with a stronger character, you'll rip through them before they can get a shot off.
Also, with a character like The Apprentice or Raphael who have good simple throws (both LT) that can ring out. The Apprentice's works great in multi-enemy matches, because if you're standing near the edge, when the next enemy runs in, you can grab them and ringout them in a single throw.
Also, in any mode where you can regen your health via HP Drain and such, as long as your character has more than their starting health (provided it's already full), you'll also get a perfect when you win.
Switching in a second character at full health to get one final shot in on a weakened enemy also credits a perfect.