If it is a lava stone gas grill all you need to do is clear all the dust from the stones and gas head & clean the grid itself.

I actually vacuum the dust from the grill, and the grid I clean with a fat remover (oven cleaner) and rinse it well in water. Do not clean the grid on the grill it self you do not want any residue on the lava stones.

Also do not clean the stones themselves they keep old flavor, My grandma god rest her soul claimed she never cleaned her grill, I know it sound strange but she was Romanian, and she use to cook in mysteries ways.