How can I make my scars from a skin graft heal?

Heal or improve? I am guessing you mean improve and not heal. Scars only result after the donor / recipient sites have healed. I am a big proponent of scar massage for the improvement of all scars, including those resulting from skin grafting. What you put on your hand before you do the massage (cocoa butter, vitamin e, mederma) is not as important as vigorous massage, twice a day. Further surgery can also help.
Scar RX. There is silicone sheets from cica care, there are creams like mederma and kelocote. Cortisone injections into the scar tissue also reduces scar formation.