Recently, I have studied a few things about low-level design from scratch.

I wrote one small document on LLD and how to approach LLD problems; what kind of problems are being asked in most of the interviews.

Here is the link -- LLD Document

This covers:

1. what is LLD?
2. How to approach the problems
3. How to explain your thoughts to the interviewer
4. How to design a Pen
5. A problem: Design tic-tac-toe

Please let me know in the comments, what should be the next.