Yes the most accurate part of your arm would be either your forearm and place the blood pressure monitor cuff near your elbow to get the most accurate blood pressure results.
The higher up your arm the blood pressure cuff is the more accurate reading and you should make sure your arm is resting firmly on something.
When taking blood pressure you should remain calm, still and quite until the blood pressure monitor takes it's reading.
When you take your blood pressure reading on your wrist it's less accurate but the forearm is a pretty accurate location for taking blood pressure readings.