GROUP BY rewrite to subqueries with easily interchangeable AND OR conditions
First clean the join syntax:

SELECT * FROM content as c
inner join tag_map as t on c.id=t.id 
inner join extrainfo as e on c.id=e.id
WHERE
#AND OR conditions here
#conditions can be very different but I would like
#to use the same query structure
#just change conditions here as necessary
GROUP BY c.id


Now substitute your and/or clauses in place of the rem'd out lines above. Then look into indexing those columns (indexes should cover all the fields in the conditions). 

These simple steps will speed up significantly. If you need further speed ups, please post before and after speedup results along with complete details of existing indexes.