First of all when you enter Campaign, you MUST be on Intermediate difficulty or above. If you struggle on that or higher, my advice would be to practice on quickplay to avoid the headache of the last part of the campaign. You can also unlock powerups to aid you in quickplay too.
To earn this trophy requires a bit extra on top of merely finishing the campaign. It's divided into three sections, each of which containing four mandatory songs. However, a fifth can be unlocked by earning a higher score. Each song grades you with up to three bars, and if you acquire 10 of the 12 possible bars, you'll be taken to the bonus song after completing the fourth in each region. This means you need to earn at least max bars on two songs, then two out of three on another. There is not a lot of margin for error, then.
To successfully rack up those high scores, you have to utilize powerups (particularly multipliers once you unlock them) and keep a combo. If you feel your score is particularly low, RESTART BEFORE YOU REACH THE END, because otherwise you miss your opportunity and if you don't earn enough bars before getting to the end of the region, you will have to begin the campaign again. My advice is play on Intermediate, although a later trophy does require you to do this on expert without restarting/failing so if you feel confident you can attempt that, otherwise once you complete Wayfarer you unlock this trophy.