google is now using the speed of your site to determine your search rankings your site needs to be as fast as it can. Along with optimising your site for search results and w3c and wcag validation you now need to optimise for speed using google pagespeed.
there are a lot of good tools out there to help you:
yahoo Yslow plugin for firefox is excellent
google pagespeed is excellent too
there is lots and lots of information about these things on the net, but ill quickly go over some of the things that will make the most difference:
put the following into your .htaccess –
# 480 weeks
Header set Cache-Control "max-age=3456000, public"
Header set Cache-Control "max-age=3456000, private"
I think the most important thing to consider is compression. it will speed up your page loading times by an order of magnitude. combined with all the other improvements that the Yslow and pagespeed plugins will tell you about it should make for your site to be as fast as it can be!
this, like the seo optimising and the validation is an ongoing process, but the more you do it the better your site becomes and the less that will go wrong with it =)