Is praying futile given that God respects our Free Will and is omniscient?

If God respects our free will and doesn't interfere in our decisions, why should we pray for things (petition)? For example, if I pray for my daily bread, God cannot force me to go to the store, buy bread, and bring it home. All these choices are decisions I must make freely. Or if I ask for a good grade on my exam, God cannot force me to study, or choose my answers. How can God help me without breaking my free will? Furthermore, He already knows the future and exactly what grade I will get (which is a part of His perfect plan), so why should I pray for a certain grade?