If you've got your list of on-page SEO services together, get your pen and pencils out cause there's a few more of those SEO services to add to the list - thanks to Google making known that site speed has become an open ranking factor.
Please note: applying each of the steps below will not only compel Google to give your website a cleaner bill of health but the other major search engines will appreciate the changes too. Although Google has come clean with respect to site speed we cannot deny that speed could one day become an important ranking factor for the other search engines - not to mention the fact that a quicker website truly helps your users experience become much better as well.
And please, to all the experienced, seasoned and highly successful SEOs visiting this thread, no flaming. Even though most SEOs take care of these parts of a website these particular tips rarely make the list of on-page SEO tips specifically as such.
I discovered the following after taking a look at page speed in the Labs section of Google Webmaster Tools.
The new tips to help speed up your website or that you can implement on your clients website can be classified as follows:
Enable gzip compression in your .htaccess file
Enabling gzip compression in your .htaccess file can substantially reduce the size of the files being sent from the server to your users computers (the browser). By enabling gzip compression within your .htaccess file you're telling the server to compress (zip) the file before it is sent to the users browser. Compressing the file can make it substantially smaller and thus substantially reduce the load time of your pages.
Simply add the following directive into your .htaccess file.
Make sure to test your website immediately after adding the above directive so as to make sure everything is in working order.# compress all text & html:
AddOutputFilterByType DEFLATE text/html text/plain text/xml
# Or, compress certain file types by extension:
Minimize DNS lookups
Straight from Google on this one: "Reducing the number of unique hostnames from which resources are served cuts down on the number of DNS resolutions that the browser has to make, and therefore, RTT delays." The entire piece of information regarding the reduction of DNS lookups is quite lengthy and technical so I'll summarize it here: Try your best, your very best to reduce the number of domains/hosts that your files come from OR try to reduce the number of external files you use on your site especially during initial load time.
Combine external CSS
This is straight forward and even slightly intuitive. It's almost second nature to cut the corner a little bit by placing all your CSS code into one file and is conducive to a faster loading website. Again one file, one call - responses to CSS calls are usually quick and combining your CSS references into one file can only benefit your site with respect to site speed. There generally aren't any problems related to putting all your CSS code into one stylesheet.
Optimize the order of styles and scripts
If you've installed Google Analytics code into your website you may have found your website loading slow from time to time due to the analytics script taking it's time to load. Google has addressed this issue with Asynchronous Tracking. Asynchronous tracking optimizes how browsers load Google's ga.js and thus shortens the load time of your pages.
Simply replacing your analytics code with the code example on the asynchronous tracking page will do the trick. Or simply replace your current code with the code below:
var _gaq = _gaq || ;
ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js';
var s = document.getElementsByTagName('script'); s.parentNode.insertBefore(ga, s);
Make sure to replace the 'UA-XXXXX-X' with your property ID. The property ID can be found in your previous analytics code or in the settings for your domain in your Google Analytics._gaq.push(['_setAccount', 'UA-XXXXX-X']);
Like I mentioned earlier, for a lot of SEOs these type of tips to help speed up your website are common sense but for many, especially the busy ones who aren't able to get updated information as quick as some of us can, especially in relation to Google and site speed, these SEO service additions can be really good as another aspect of a proposal for SEO services and/or as a part of a thorough website audit.
The information above was gathered through the Page Speed Suggestions section of the Site Performance section in labs for Google Webmaster Tools and on Google's page about asynchronous tracking. If you've discovered other tid-bits related to speeding up your website but not specifically related to any particular CMS feel free to post your speed tips below for the rest of the members.
The full list of site performance suggestions will give you a complete set of new SEO tools and more importantly, responsibilities, that you can apply to your website, or as a services for your current and future clients.