Optimize multiple JOINs in MySQL

Optimize multiple JOINs in MySQL

I have this MySQL which should be correct syntax:
select c.cat_id,c.cat_name as cat_name,
c.cat_desc, c.cat_image, mi.filename,
l.link_id, l.user_id, l.address,l.city,
l.country,l.link_created,l.link_desc,
l.email,l.fax,l.link_hits, l.link_modified,
l.link_name,l.postcode, l.price,l.link_rating,
l.state,l.telephone,l.link_votes,
l.website, l.link_id, l.link_visited, cf.value
from j25_mt_cats as c,
j25_mt_links as l
LEFT OUTER JOIN j25_mt_cfvalues AS cf ON (cf.link_id = l.link_id),
j25_mt_images AS mi,
j25_mt_cl as cl
UNION ALL
select c.cat_id,c.cat_name as cat_name,
c.cat_desc, c.cat_image, mi.filename,
l.link_id, l.user_id, l.address,l.city,
l.country,l.link_created,l.link_desc,
l.email,l.fax,l.link_hits, l.link_modified,
l.link_name,l.postcode, l.price,l.link_rating,
l.state,l.telephone,l.link_votes,
l.website, l.link_id, l.link_visited, cf.value
FROM j25_mt_cats as c,
j25_mt_links as l
RIGHT OUTER JOIN j25_mt_cfvalues AS cf ON cf.link_id = l.link_id,
j25_mt_images AS mi,
j25_mt_cl as cl
where cf.cf_id = 40 and cl.link_id = l.link_id
AND mi.link_id = l.link_id AND mi.ordering < 2
AND c.cat_id = cl.cat_id and c.cat_published = 1
AND c.cat_approved = 1 and l.link_published = 1 and l.link_approved = 1
AND cf.link_id IS NULL
ORDER BY RAND() DESC;
The query eats up 3GB+ in the tmp directory and ends up timing out. I'm
missing something here, how can I increase the efficiency? My goal here
was just adding onto an existing query to grab a value from an additional
table (j25_mt_cfvalues).