2 of 5 added 24 characters in body

Optimization on table selected where primary key

I have this query:

FROM wp_dev_term_taxonomy, wp_dev_terms 
WHERE ((wp_dev_term_taxonomy.taxonomy = 'category')) 
      AND (wp_dev_term_taxonomy.term_id = wp_dev_terms.term_id);

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

wp_dev_term_taxonomy.term_id = wp_dev_terms.term_id

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