Performance

I come from a Sybase background and have just started working with
Postgre. Are there any books or tutorials that cover general performance
issues for beginners? I don't just want to start creating databases and
tables or writing mad queries without really understanding what is happening
in the background. I know quite a few tips and tricks for Sybase but I don't
think that much of it is relevant on Postgres. I would like to know how
the query optimizer works, i.e. does the order of tables in the from
clause make a difference in speed and how does indexing work on Postgres?
Any help pointing me in the right direction would be appreciated.

Many Thanks
Jeandre