To solve the equation \( ax - 7 = 26 \), the best first step would be to add 7 to both sides of the equation. This will help to isolate the term containing \( x \).
So, performing this operation:
\[ ax - 7 + 7 = 26 + 7 \]
This simplifies to:
\[ ax = 33 \]
Now, you can proceed to solve for \( x \).
Therefore, the best first step is to add 7 to both sides of the equation.