1) If you have MONyog installed then start follow advisors in 'Monitors Advisors' page for various buffer settings – both for the server level and the storage engine(s) level (with a Forums software running I will assume that MyISAM is used). The default settings that the server ship with are much too small for a production server.
2) You should try use the MySQL 'query cache' if you don't already. With Forums it is very often a few very popular posts the draws a majority of the request. Also here MONyog will give you advisors on how to configure the settings. But here you may encounter the problem that the software does not consider that user may use 'query cache' and do not use the 'SQL_NO_CACHE' clause for queries that should not be cached. But give 'query cache' a try anyway.
3) Ensure that you MySQL server is not a debug build (they are slow) and if you do not need the general log – what you probably don't – then turn it off in order to reduce disk I/O (but it may be turned off already)
4) You may try to identify slow queries with the MONyog 'query analyzer' – just one more index to a table etc. may improve performance. But is is always problematic 'hacking' such standard applications, as it may very well cause trouble upgrading the software.
