I have this query:

FROM wp_dev_posts, wp_dev_postmeta, wp_dev_term_relationships 
WHERE ((post_type = 'projects') OR (post_type = 'post_cost_codes')) 
    AND (wp_dev_posts.ID = wp_dev_postmeta.post_id) 
    AND (wp_dev_posts.ID = wp_dev_term_relationships.object_id);

My question, is that when I have this in the where:

    wp_dev_posts.ID = wp_dev_term_relationships.object_id

What's the correct way to optimize this? Am I better to use joins? Do I set index's? Do I use foreign keys? On a large database this is actually take a few seconds to run.
SQL newbie here.