Each deity has their own Gāyatrī mantra, a short 3-line mantra that invokes their power and blessing in a very potent way.
This is the Gaṇeśa Gāyatrī mantra. Before you recite it, you may want to take a gentle, attentive, upright posture. Let your attention and energy quiet, and feel the center of your being. Visualize Śrī Gaṇeśa as you listen and chant.
oṁ ekadantāya vidmahe | vakratuṇḍāya dhīmahi | tanno dantī pracodayāt ||