I have the following two queries which really do need optimizing although not being a mysql expert I am unsure how to do it myself. Can anyone help?
What do you mean optimization? I think that is as optimized as your going to get it. The query itself can't be optimized, but I think you confused that with the tables in the database.
Nothing you can really do for the actual queries. Make sure you have a unique index on: sites.username, and possibly one on stats.unq_pv_overall. Is there a specific problem you're experiencing?