When you're learning how to complete the square, there are some common mistakes you should try to avoid:

1. Remember to Keep Both Sides Equal: Always add or subtract the same number from both sides of the equation. This helps keep everything balanced!

2. Finding Half the Coefficient Correctly: Make sure you correctly find half of the linear coefficient and then square it. For the expression $ax^2 + bx$, it should be $\left(\frac{b}{2}\right)^2$.

3. Don't Forget the Constant: Be careful not to overlook the constant when you rewrite the equation. Forgetting it can mess up the entire problem!

If you can spot and fix these mistakes, it will make a big difference in your understanding!