It's "optics", can't you "see"

Optics is considered as one of the simplest portion in JEE syllabus.
Optics requires quite a bit of memorization and a good command over
basic high school mathematics (mainly geometry and algebra). One
should be comfortable with calculating unknown angles / distance etc.
The problems in optics are generally simple and easy to solve. But
there is an obstruction on the way – silly mistakes. Since the
questions are mainly mathematical, it’s very easy to make silly
mistakes. So, it is advisable to practice plenty of questions from
optics.
Also, there are quite a bit of formulas involved in geometrical optics
part (u-v formula for lenses/mirrors, laws of reflection and
refraction, etc). So, it’s better to understand the derivations as
well which will surely help in tough situations.
Keep in mind that optics portion has a huge weightage in JEE and so, a
candidate aspiring for a good rank cannot afford to give away marks so
easily.
As usual, we will go chapter wise (as mentioned in JEE syllabus):

•       Rectilinear propagation of light: This portion mainly includes the
elementary properties of light. The basic properties about the nature
of light coupled with laws of reflection and refraction form the basic
framework of the entire optics. So, students should understand these
topics very well and practice ample of questions. Simple ideas can be
effectively used to frame complicated questions but those who have a
good understanding of basic concepts won’t face any problems.
The ideas of total internal reflection and deviation of light by a
prism are simple but slightly theoretical. So, one must read enough
theory for these concepts. Good questions are asked from total
internal reflection and the questions asked are generally “new” ones.

•       Reflection and refraction at plane and spherical surface: The ideas
covered in the last chapter will be improved and the concepts of
reflection and refraction at curved surface will be introduced. As
before, the ideas taught in this chapter will be used in the next
chapter. You will be taught a couple of equations which will be used
to predict the path of reflected/refracted ray. There will be a few
derivations involved which are simple yet important and must be
understood very well.

•       Spherical mirrors: The idea of reflection of light will be improved
upon to develop the idea of reflection of light from spherical
mirrors. A new equation called the u-v equation for mirrors will be
introduced. There will be several cases of position of objects and
associated images. Students must keep in mind the properties of images
formed for a given position of object. The idea of lateral
magnification helps a lot to predict the size of image. Proper care of
sign convention must be taken to avoid silly mistake.

•       Lenses: The idea of refraction of light at a curved surface will be
used to build up the concept of lenses. A new equation called the u-v
equation for lenses will be introduced in this chapter. Note that the
u-v equation for lenses is quite similar to the u-v equation for
mirrors. So, students should ensure that they do not interchange the 2
equations while solving problems. It’s very easy to make silly
mistakes here and it has been seen that even very vigilante students
make mistake here. One must take care of appropriate sign convention
while solving questions of lenses. Mind bending questions are also
asked from combination of lenses. One must keep the idea of “power of
a lens” in mind while solving problems of combination of lenses. The
idea of “effective focal length” helps a lot in solving problems
involving lenses separated by a distance.

•       Combination of lenses and mirrors: Most questions of optics are
asked from this portion. If the student is weak in any of above
topics, he/she is likely to face problems in solving JEE questions. So
to solve (apparently) complicated questions, students should focus on
the basic ideas taught in the previous chapters and integrate them in
the correct way.

•       Wave optics: “Huygen’s principles” form the basics of this chapter.
The idea of wavefront is the basic idea and must be understood very
well. Students tend to ignore this portion and the JEE paper setters
are pretty much aware of this so they have started asking very good
“paragraph” type questions from this portion. So, avoiding this part
may significantly affect your rank.
Next comes the famous YDSE – Young’s double slit experiment – a very
important idea. Every year there is at least 1 question from YDSE.
Very frequently questions on “modified YDSE” are also asked. For
example – a glass slab is introduced in front of 1 or both slits. The
key to solve this problem is the idea of “phase and path difference”.
Students are advised to practice variety of questions from YDSE
portion.

To summarize, optics covers a variety of simple ideas which are very
common in JEE. So, students aiming for a seat should not ignore the
optics portion. Solving as many problems as possible will surely help
you to get a firm command over optics portion.

Recommended textbooks: HC Verma, DC Pandey, NCERT, Resnick Halliday