What is the best technique to optimize a site?

What I have found to work best is clean code, well crafted clean code. Is the file size of your pages more than 20Kb? Look into removing excess code to make them smaller. If your site takes a long time to load, look at making the file size of the images smaller. If you have lots of solid color, look at using 1 pixel square images stretched to the height and width you need. You might even try cutting larger images into several pieces. Sometimes one large image takes longer to load than three or four smaller images. Images that are reduced to the smallest resolution without losing clarity or sharpness will load faster.

After that has been tried you might look into your hosting company. Is might be that the server your site is hosted on is slow or their connection is slow. Do they only have one pipe to the Internet or several? Are they on a T1, T3 or OC line?

Hope this helps.