When should I start applying acne scar ointment?

I'm worried that a wound will form on the troubled area and leave a scar.

I'm wondering if I can apply it right away while it's still slightly red...

Or I'm wondering if I have to wait until the scab falls off completely for it to be effective!

Do you have any scar ointments or care methods you would recommend?

Please leave some advice in the comments. This is a must-read!