One fact that's often overlooked is the fact that Beacon of Light has *60* yard range, even though paladin heals have a 40 yard range.
So if you're assigned to heal a target that occasionally goes out of range, keep Beacon up on them, and heal people closer to you. This gives you a little more leeway in moving. You don't have to move right away to keep pace with your target, you can move a bit later. Or sometimes you don't have to move at all, if they will come back in range.
This is a particularly useful tactic for fights where someone has to go pickup adds and bring them back to the group, as they'll often only be out of range for a few seconds. Beacon of Light can even be cast when the target is up to 60 yards away, so you don't even need to refresh Beacon early.
This is a small tip if you are having range issues as a paladin healer. Choose your Beacon target wisely. Sometimes the main tank is not the best choice.