Here are some tips for tuning postgres performance using the EXPLAIN command:

• Use “EXPLAIN (ANALYZE, BUFFERS) SELECT …” as of PG 9.2.
• Paste the output into this service to highlight areas of concern: http://explain.depesz.com/
• Learn about EXPLAIN from the detailed documentation: http://www.postgresql.org/docs/current/interactive/using-explain.html
• This Wiki page has more pointers to other tools and tutorials around EXPLAIN: http://wiki.postgresql.org/wiki/Using_EXPLAIN