Trick to learn ray diagram of lens ray diagrams...

Solution
For this you need to understand basics of ray diagram rules

• An incident ray parallel to the principal axis passes through the focus after refraction
  by a convex lens.
• An incident ray parallel to the principal axis appears to diverge from the focus after refraction by a concave lens.
• An incident ray passing through the focus goes parallel to the principal axis after refraction by a convex lens.
• An incident ray heading towards the focus goes parallel to the principal axis after
  refraction by a concave lens.
• An incident ray passing through the optical center emerges undeviated from its actual
  path after refraction through both concave and convex lenses.