looking to speed up SELECT ... LEFT JOIN query

Hi,

I have a working SELECT statement using LEFT JOIN but I'm hoping
someone can suggest something that might be a bit quicker (currently 3
seconds for result).

SELECT * FROM ((table1 LEFT JOIN table2 USING (custno)) AS j1
LEFT JOIN table3 USING (custno)) AS j2
LEFT JOIN table4 USING (custno)
WHERE custno='$custno';

The primary table is table1, the key for all tables is 'custno'. I
need the LEFT JOIN because any one or all of the other tables (table2,
table3, table4) might not have corresponding data.

Regards,

Trey Ackerman