The limbs and the names
A common order is: "Om Ganeshaya namah, padau pujayami", the feet; Vighnarajaya, the knees (januni); Akhuvahanaya, the thighs (uru); Herambaya, the waist (katim); Lambodaraya, the belly (udaram); Gaurisutaya, the chest (stanau); Ganadhipaya, the heart (hridayam); Sthulakarnaya, the throat (kantham); Skandagrajaya, the shoulders (skandhau); Pashahastaya, the hands (hastau); Gajavaktraya, the face (vaktram); Vighnahantre, the eyes (netre); Shurpakarnaya, the ears (karnau); Phalachandraya, the forehead (lalatam); Sarveshvaraya, the head (shirah); and finally Vighnarajaya, the whole body (sarvangani pujayami).
Each name matches its limb: the remover of obstacles at the knees that walk the path, the one who rides the mouse at the thighs, the big-bellied at the belly, the son of Gauri at the chest, the one with the noose at the hands, the one with ears like winnowing fans at the ears, and the one with the Moon on his brow at the forehead.
How it is done
With the right hand, offer a few grains of akshata, a flower or durva towards each limb of the image as its name is spoken. Lists differ slightly between books; families follow their own. Many priests then go on to the 21 leaves, the 21 flowers and the 21 durva offerings, and finally the 108 names.