Install A Cache
Optimising your images reduces their file size without losing picture quality. You can either use a program that does this before uploading your images to your server (such as ImageOptim for the Mac) or you can use a WordPress plugin that does this after uploading your images.
Remove Query Strings From Static Resources
By default the Gravatar icons are loaded from the Gravatar server, you can cache these and host them from your own server to reduce page load time using the Optimum Gravatar Cache plugin.
Using A CDN
My Site Is Still Slow
Install the Query Monitor plugin to see if there are any database queries that are slowing down your site.
Having multiple plugins installed and activated on your site can slow it down. The more plugins you use, the slower it will be. Please disable all the plugins on your site except for those required by the theme.
Now clear your browser cache and see if it speeds it your site up. If it does activate the plugins one by one and check the site speed each time to try and find out if a specific plugin is causing the slow down.
Unfortunately there are plugins out there that can slow down your site, if you happen to find one please contact the plugin developer and report it to them.
If you site is running slow and you are hosted on a shared server you should consider moving to a VPS or dedicated server. A shared server distributes the server resources across many sites leading to a noticeable slow down when sites on the server have a lot of visitors. If your own site is getting a decent number of visitors you should definitely not be using a shared server. With VPS and dedicated servers you have your own server resources that are not used by any other sites.
Even if you are using a VPS or dedicated server, some web hosts are better than others. Speak to your web host about increasing your server specifications or consider moving to a different host. I recommend WPEngine.