Some Tools to Help Reduce Page Download Size
Reducing our page download size can help improve the speed of our website. Here are some tools and principles to help with reducing page size.
First you want to run the site though the Google’s PageSpeed Insights It will give you some suggestions on how to optimize for mobile and desktop views.
Another similar tool is Pingdom, which shows you a waterfall graph of the load time of various assets.
It might suggest things like concatenating and minifying CSS and JS. Before minifying your CSS, you might want to remove unused CSS rules and then run it through CSSLint.net. It will help you write better CSS code.
Then you can run the CSS through minifycss.com or other such online tools. It is perfectly fine to run your code through these online tools because afterall the CSS and JS code are publicly visible on your site anyways. It is not like you are uploading some propriatary code onto some unknown server.
You also want to optimize image size. Use JPG for photos and flattened PNG for other images. Then run the image through Smush.it There are many other tools that can optimize images (especially Photoshop and Fireworks). But sometimes it is nice to have an online service like Smush.it (and it is by Yahoo!)