1. Draw y=f(x) on the right-half of the coordinate axis (quadrants 1 and 4)
2. Flip everything below x-axis to above (like when you draw y=|(x-1)^2 - 1|), giving you a curve in the first quadrant only
3. Mirror it to the bottom
4. Mirror the new curve to the left
(As a check... the curve in each of the 4 quadrants must look "identical")
Explanation of steps:
1. Draw y=f(x) with x>=0 only
2. Draw y=|f(x)| with x>=0 only
3. Draw |y|=|f(x)| with x>=0 only
4. Mirror it about y-axis to get |y|=|f(|x|)|