While this is too simple for real world acid base stuff, it works great for exams where numbers are usually exaggerated.
Remember these normals:
pH=7.4
pCO2=40
HCO3=20
Step 1: Determine how your values compare to the normals
Step 2: Is it acidosis (pH<7.4), or alkalosis (pH>7.4)?
Step 3: ROME: Respiratory Opposite, Metabolic Equal. If pH and CO2 (or HCO3) move in opposite directions, it’s a respiratory problem, if pH and HCO3 (or CO2) move in the same direction, it’s a metabolic problem.
Step 4: If both pCO2 and HCO3 values changed then it’s compensated, if only one changed it’s uncompensated.