I put Archie in the jolly jumper on the bathroom doorframe every morning while i have a shower, at about 6 months (before he had teeth) i used to give him a gum massager (made by nuk, looks like a toothbrush but its rubber) then at 8 months when he had 2 teeth i bought a baby toothbrush and he uses that while i brush my teeth.

I just do it to get him into a good habit, plus he has lots of fun especially when hes teething.