If you already know T-SQL, using more standard SQL should be a breeze. I get confused with T- more because of all of the @ signs and varchar's etc. More standard SQL such as you would use in Access (SELECT * FROM tblMain) seems alot cleaner to me.
If you have MS Access, you can use the standard Northwind database and build queries in the SQL view of the QBE using straight SQL. I can't think of a better way to practice. Also, it is just test data so you really can't mess anything up.
Good Luck!