it's easy for someone who knows what he do... i usually know... for someone ot aware of all the little webmastering tricks, it's a real mess to start with.

but basically, you need to have your tables optimized, datastore rebuilt, split your forums in sub-forums when possible/needed, you also need to switch to FULLTEXT search when it's not, so your database is not filled with millions of indexes... lowering some datelines and setting some features to lower priority is also needed to make your searches faster...