For final fantasy 5 and most of the other final fantasy games I use this technique to level the characters faster.
1. Walk around until you get into a random battle. 2. Make sure your characters are strong enough to kill the enemies without dieing. 3. Kill all your party members except the one you are levelling. 4. Carry lots of tonics so you can heal. 5. Repeat with all the characters until the levels are high enough for your game.
Because their is only one character alive they get more experience then they would when their all alive.