Here's a tip I'd never even considered from SL user Jessica Pixel's Plurk: If you're the kind of person who likes an expressive avatar, you might want to make yourself a special shape to get the most out of a toothy smile emote. Jessica's own animated gif, shown above, illustrates the differences between her typical shape and a smile-ready shape pretty well. Depending on the dimensions and features of your facial shape, Second Life's built-in grins might look compressed, or just not quite as nice as they could. Not every shape will need it (and not every player will want it) but for those that are interested few tiny tweaks to the mouth area are all you'll need.
As most fashion-minded SL users know, multiple subtle tweaks of the same avatar shape can be a pretty crucial part of your wardrobe, especially if you want to fit perfectly into your favorite mesh attire and accessories. Likewise, shape tweaks can help make your avatar look more consistent across a variety of skins. So if showing your avatar's pearly whites is a priority, try this out for yourself.