ORDER BY takes columns: a list of column names (or expressions), and you can add ASC (the default) or DESC (descending order):
SELECT TOP 5 * FROM rave.dr3 ORDER BY rv
SELECT TOP 5 * FROM rave.dr3 ORDER BY rv DESC
SELECT TOP 5 * FROM rave.dr3 ORDER BY fiber, rv
Note that ordering is outside of the relational model. That sometimes matters because it may mess up query planning (a rearrangement of relational expressions done by the database engine to make them run faster)
Select the (rows of) the 20 brightest stars in the table fk6.part1.