Patent ID and date
The identity of the patient should be checked before interpreting any X-ray. The date of the investigation should also be noted and even the time is relevant if the patient has had more than one X-ray on the same day.
Image projection
Check if a posterior-anterior (PA) or anterior-posterior (AP) projection was used, and note if the patient was standing, sitting or supine? Was the mobile X-ray machine used?
Image annotations
Useful information is often annotated on the image. If the projection is not marked, it is likely to be a standard PA view. If there is one, check the side marker is correct.