Question

I need help studying lense diagrams
only for convex and concave lenses
are there any helpful hints or tricks to memorize them?

Answer 1

Learn the basic rules so you just do them:
Draw 2 lines only.
From a distinct point on your object (usually the 'top')
1. draw a line parallel to the optical axis to the lens,
2. Draw a line stright to the centre of the lens
What happens then depends on the lens.

Convex:
1. This line will now travel through the lens and refract through the focal point.
2. This line will keep going through the lens on the same path.
Concave:
1. This line will travel through the lens but refract outwards, so that the line traced back would go through the virtual focal point.
2. This line also goes straight through!
If your object is on the optical axis, then that part of the object will be touching the axis. See my diagrams: