As part of application processing Canada Immigration Medical Exams requested, if you receive Medical Exam request you are already halfway through your application. Normally CIC give clear instruction how and where Medical Exam has to be done. For Express Entry applicants Medical Exams has to be taken before submitting the application.
Normally there no special procedure to follow, however following notes may help
Canada Immigration Medical Exams Notes
1. Best thing is having sound sleep prior night.
2. Avoid schedule your test if you have cough so that chest x-ray is clean.
3. Drink lot of water before test that clean urine and kidney.
4. Share your all your medical situation including surgery.
In case anything found wrong that does not mean that your application will be rejected that may delay your processing time for more clarification between and doctor and CIC.