This has to be done after sunset. To ward off illness do the following

Place Lord hanuman pic or statue or go to a Hanuman temple.
Light a mustard (Sarso) oil lamp

Chant the following 

Jai Shree Ram (3 Times)
Om Ramdutaya Nama

State of Intention 

Divine Lord Hanuman I am chanting this prayer for healing _____ (Mention the name of the person who is sick)

Chant Hanuman Chalisa continuously 7 times.

Let go of results, whatever is the highest good for the patient will happen. Listening to Hanuman Chalisa and Durga Kavach wards off all kinds of negativity and gives emotional strength to face any situation. The above ritual is NOT meant to replace any medical consultation or medicines.