Hello Subhayan

Usually the selection criterion goes like this (in descending order):

Academic GPA/CGPA/%age as well as ranking in your batch

Undergrad university

SOP

Research ex/Work ex

GRE

LOR

These other factors will vary from case to case:

Final Year Project

Internship and papers

Co/Extra-curricular

Prof Letting

Problems people might face:

Backlogs

Year Gap

Plagiarism