I really didn't start brushing DS teeth till he was a year old...we do it when he takes his bath when the water is filling. He's so occupied with playing in the water I don't even think he notices I'm brushing his teeth.
We didn't brush my DS teeth until he started watching us brush our own. After DS bath, DH would brush his own teeth, and have DS "practice" brushing his teeth. We would then quickly finish them. He is now 5 years old and his teeth are fine. Dentist said it is more just to start a habit for when he is older, because their teeth are so far apart it is difficult for cavities to form anyway.
I do'nt actually brush his teeth yet (he only has two little half teeth anyway), but I give him his toothbrush to play with first thing in the morning (while I brush my teeth) and then after his bath while I'm dressing him. He just plays with the toothbrush, chewing on the bristles and also the handle, but it is getting him used to the idea.
Re: How am I supposed to brush his teeth?