If it's a wordpress site, I found the best thing for me was to set up Cloudflare in front of the site, because they can cache a lot of requests. The next best

If it's a wordpress site, I found the best thing for me was to set up Cloudflare in front of the site, because they can cache a lot of requests. The next best thing is making sure APC is set up on your server. I've also had success tuning settings in Apache to help with memory use, but that's a lot more time consuming.