• First check whether it is a mirror or lens; Incase of mirror bouncing of light happens (Reflection) and in the case of lens, bending of light happens (Refraction)
• Next find the type of mirror or lens ; Mirror could be plane, concave or convex; Lens could be concave or convex
• In case of mirror, marks the polished side correctly; If it is lens, draw the lens appropriately
• Mark the centre of lens / mirror as the pole of the lens /mirror as P. Draw the principal focus passing through the centre of curvature and the pole
• Mark the centre of curvature as C and the focal length as F on the principal focus such that  the radius of curvature as r = 2f
• Draw the object and object distance as u
• Draw rays of light from the object to the mirror / lens
• Similarly depending on where the object is present, draw the image and the mark the image distance as v
• All rays have to be given proper direction using arrow marks otherwise the diagram is invalid

 

Take the case of concave mirror; Go through the table which gives all the conditions for the object position. Trace the image position. You will get a feel of drawing a ray diagram.