It is one of the easiest topic to be covered and has a sure question in both JEE-mains and JEE- Advanced. It generally contains formula based implementation which attains a gain to take lead as calculations are not very lengthy or time taking.
Every year there is at least one question that comes in both JEE-Mains and JEE-Advanced from progression and series section. Also, since the questions are generally just formula based implementation they are very scoring. Many times the questions are also blended with concepts of differentiation and solution of triangles, so this is an important section which may be useful for scoring good. The important parts of this section to be focused are discussed below.
Observing the trend from last year papers, it can be concluded that general understanding of arithmetic, geometric and harmonic progressions along with some basic formulas of sum of natural numbers, squared numbers and cubed natural numbers may be useful for solving questions. Besides this, properties of A.P., G.P. and H.P. are asked directly many times. In addition to this, inter-relation between these three can be asked. These are majorly the important topics which should be studied and one should not neglect these. For taking an edge over others, this is a wonderful chance as an easy topic makes your score good. Should not leave any topic from this chapter and must understand concepts too rather than just learning.