As always, try to take a high level look at the profiler's results.  For
example, if it tells you that one arithmetic operation is the big cost,
try to decide whether you can not do the computation, or change the
algorithm to do that task fewer times before trying to get a ++ or -- to
execute faster.

In Java, the above vague advice usually translates to looking at when
and how you are creating objects, and making sure you do not have
excessive synchronization overhead.  Also, a few Sun classes are quite
lame, and worth rewriting.  (If, and only if, they are taking
appreciable time...)

Then, once you know your algorithm is appropriate, tune the lines of
code that matter.