Proof by Contradiction

Definition

Suppose we want to show a statement of the for $p$ is true. Suppose we find a contradiction $q$ such that $\mathrm{\neg }p\to q$

Because $q$ is false, but $\mathrm{\neg }p\to q$ is true, we can conclude that $\mathrm{\neg }p$ is false, which means that $p$ is true

How can we find a contradiction $q$ that might help us prove that $p$ is true in this way