There is a nice tool like Percona’s ‘pt-query-digest’ tool at http://www.percona.com/doc/percona-toolkit/2.2/pt-query-digest.html, which will automatically parse the slow_query_log and analyze it for the slowest queries.
you run the command
pt-query-digest slowquerylog.txt
Wich should output a summary and a list of the longest-to-execute queries.