Read the data sheets for the regulator you are using. Most specify a maximum distance between the regulator and the input and output capacitors to ensure no oscillations from the regulator. If in doubt go for two large capacitors (100 uF or more) adjacent to the regulator input and output and make the PCB traces as fat as possible for minimum impedance. Make sure you have a big safety margin on the input capacitor voltage rating. Automotive +12 volts should have a minimum 50 volt rating on the input capacitor, preferably 100V.

HTH
BrianT