You should have a clear idea of how backtracking works (in your problem) and develop intuition for it, perhaps start with a simple case on your paper to simulate it effectively. Understand what happens when it backtracks, the pattern, the recurrence, and observe various codes to gain insights into different approaches

Pen and paper

Go and solve Usaco complete search with recursion problems and you will be fine

if you can find the approach and cant code my new blog about backtracking might (or might not) be useful for you, https://mirror.codeforces.com/blog/entry/131470, practicing is very important

Write a sudoku solver.