After that it's a question of adding and tweaking geometry to make it look realistic. You can smoothshift inwards to make the ear canal, and outwards to produce all the little ridges and so on. Definately look at some photos! www.fineart.sk is a good resource for that. And practice, practice and practice some more. Don't get discouraged if it doesn't work too well the first few times!

I hope this helps a bit! - Baz :o)