In Paper Mario: The Thousand-Year Door, you'll want to be consistent in leveling up your Badge Points (BP) and collecting badges, which unlock different abilities that can help in battle. You'll find badges in the overworld, or you can buy them from certain vendors. However, most of these unlock after you've visited the Thousand-Year Door. The Pretty Lucky badge is one that you can obtain before Mario formally starts his quest. Pretty Lucky is a good "beginner" badge due to its effects in battle. As you level and unlock more badges, you can swap Pretty Lucky out for something stronger.