This is the easiest way to learn your music quickly, and how to learn it right. After you’ve located your music, look for the publisher (probably listed at the bottom, beneath all of those runs you’re supposed to ace in three weeks). Now, hop on your laptop and do a quick Google search of that publisher, and chances are good they have a website where you can type in the name of the song you’re looking for. If you’re lucky and it’s JW Pepper, which most marching band arrangements are, they provide audio files of the pieces they sell. Listen to it.
Listen again, and this time focus on the sound of your instrument. (Those runs sound so cool!)
Listen again, following along with your sheet music. (Those runs look so hard!)
Most marching band shows are less than 10 minutes long, so if you listen to it three times you’re looking to spend less than half an hour on it. However, if you do it often enough (read: every day) you’ll get to the point where you’ll have the overall sound of the show memorized. You may even find yourself walking around humming parts of it instead of the chorus of Bad Blood. Maybe.