Multi-user Applications

I am b-testing a community site, with currently 1,000 or so membership,
and low concurrency, say no more than 5 on-line at once.

The site is hosted on a shared server, which is sufferening from
intermittent accute slowness, affecting all other hosted sites as well as
mine.

The finger of suspicion is pointing at me and possible sloppy code. As
this is the first site I have done of this nature, could someone recommend
reading matter (knowledge bases etc), especially coding samples, in
connection with data connections (opening and closing connections and
objects) and record locking issues, which if improperly coded, could
contribute to throughput bottlenecks due to inefficient use of resources so
that I can check out my pages and correct any nasties..