You do not need to prepare for this exam especially. However, you have to change into a hospital gown and remove jewelry and piercings before the scan. Tell your doctor if you have artificial heart valves, implants, plates, prosthetic joints or limbs, or stents in your body since an MRI machine uses magnets.
Also, inform your doctor if you have had a pacemaker so they can use another imaging exam to inspect your joints, such as a CT scan. However, some models are re-programmable, so they're not a hindrance to the scan.
If you're claustrophobic, being in the MRI machine can be triggering. In this case, you can get anti-anxiety medications before the exam.