Vitamin E works wonders, when I get tattoo clients coming in that have scars that are either to fresh or still very pink I usually tell them to massage the tattoo twice a day with it to help.
There's many other methods, to many really to type here your best bet it so research online or just try the Vit.E
The issue with tattooing scars is if not fully settled pigment can actually spread through them... Suddenly the tattoo that is supposed to cover the scar brings it out even more.
Another option I use personally and know many who have is Emu oil :
http://www.emuoilcanada.com/
It's a really great working alternative and I've used it on some big scars, same as the Vit.E just massaging it into the scar a few times a day. Breaks up the scar tissue quick and helps everything settle