If like me you want to focus on getting just the novice achievement and don't plan to go for the other fight challenges, then you can work on the easy ones. I focused on overhead and aerial attacks by doing a jumping attack to open most combos. I also knocked out 10 blocks, 10 throws, 5 combo breakers, 10 Shadow moves, and some of the lower manual and auto combo challenges. Most characters have some simple super moves you can do 10 times and 50 times each to knock out some more easy ones. As you are doing all of this, you should be working toward the total combo hits challenges as well as getting some of the juggle hits challenges without even trying. You can do this in any mode, really, but I got all of mine while beating 10 survival opponents with each character.