If you're really after learning good OO knowledge and style I can't help but recommend study the things that Bertrand Meyer has to say about it in "Eiffel, The Language" , and play around with SmartEiffel a bit. The Concepts of OO-Programming, not the least Programming by Contract, as explained and to a great deal coined by Meyer, are leading IMHO to best practices in every oo-enabled language.

I don't know smalltalk very well, but from what I know, some of the others here are right, that it will make a good starting point too.

regards,
tomte

Hlade's Law:

If you have a difficult task, give it to a lazy person --
they will find an easier way to do it.