There are a lot of answers to the question 'I'm an accidental DBA - where do I start?' - but there are not so many for accidental SQL developers... The ones who wrote a query once, and were instantly tagged as the 'expert'.
I've been using SQL Server for about 11 years now, and I'm still learning new things, by following the people whom I respect on the net, reading their blogs etc. Participating in this community has also helped enormously.
But, for somebody just starting on the path - where would you send them to learn the ropes?