Just make sure you get a nice soft toothbrush (they usually have an age range on them so you know you're getting the right softness, I got a really good one from asda that has a really short, wide handle that they find easy to hold as well). Put a tiny amount of toothpaste on the brush, like a small pea size amount, then just gently massage the tooth with it, if it's just one tooth then just gently brush it with circuar motions. You'll probably find that he will bite down on the brush so just try and keep it moving all the time. You might find that he hates it at first (I know Felix did), but I now have a toothbrushing song which I sing as we do it and it makes him laugh which makes it easier to brush his teeth haha xo