I always get confused with that equation.
pH = pKa + log[A-]/[HA]
pH = pKa - log[A-]/[HA]
pH = pKa + log[HA]/[A-]
pH = pKa - log[HA]/[A-]
Two of the above are correct and they have different signs. I remember it by actually trying out the equation (e.g. adding acid, HA, should lower pH, not raise it).. only takes about 30 seconds on the exam and it's worth it if you don't want to remember a wrong form.