B.Tech Computer Science and Engineering

First and foremost focus on basics, any programming language like C, CPP, Java, Python, etc. Data structures and algorithms
Networking
Database
Operating systems
Problem-solving skills
Pointers
Topics
Linked List
Stack & Queue
Deque
Trees
Heap
Recursion
Itself one of most important topic. (Both interviews as well as Competitive programming)
Time and Space Complexity Analysis
OOPS
It is quite handy if u have in depth knowledge [go through atleast one of the good books completely] of based on any of the OOP languages (Java/C+) and also try to get proficient in coding in one of these languages besides C. To have knowledge of both will also be quite handy. DBMS
OS- (very important)
Computer N/W-
Algorithms
Advance- (Flipkart, Direct and Amazon)
1)Advance data structures- (Segment tree, Tries, BIT, Suffix Array, heap)
2)Algorithms (Djikstra, Floyd Warshall, Euler path, hamiltonian path, KMP, MST, Union Find Data Structure)
3)Combinatorics (Recurrence Relation)
4)DP
Do practice coding on online platforms and do projects related to higher tech subjects- web, python, android, ML, etc. Participate in college events - It will make companies think that you are active. If you are organizers of any event or organisation in your college, that will be an added advantage
Know programming very well! - Check out for various cases (not so common). It will be a great advantage if you are expert in something else such as php,. Net, android etc. Develop algorithms. - The skill to develop algorithms is really important. Try to solve various problems. It will help you a lot.
Reasoning is required.
Basic Maths, aptitude may be evaluated! So prepare in those fields.
Be confident.