Ideas to improve website loading speed?

Question

Are there any ways in which I can improve the loading speed of a website?

I know that Google is really pushing loading speeds and with the popularity of mobile websites it's now imperative that sites load quickly.

Answer 1

1. Yahoo's tips for improving page sped
2. Google's tips for improving page speed
3. If you're using PHP, Google's tips for making PHP faster

Here's a basic list as comprised from Google's Page Speed addon (here's Yahoo's YSlow):

• Leverage browser caching
• Specify image dimensions
• Avoid CSS @import
• Avoid bad requests
• Combine images into CSS sprites
• Defer parsing of JavaScript
• Enable Keep-Alive
• Enable compression
• Inline Small CSS
• Inline Small JavaScript
• Make landing page redirects cacheable
• Minify CSS
• Minify HTML
• Minify JavaScript
• Minimize redirects
• Minimize request size
• Optimize images
• Optimize the order of styles and scripts
• Prefer asynchronous resources
• Put CSS in the document head
• Remove query strings from static resources
• Serve resources from a consistent URL
• Serve scaled images
• Specify a Vary: Accept-Encoding header
• Specify a cache validator
• Specify a character set
• Defer loading of JavaScript
• Remove unused CSS
• Use efficient CSS selectors

I strongly recommend using either Google's or Yahoo's page speed add-ons to test out your pages. It's fast and easy to do and offers clear guidance on how to improve your page speeds.

update

As recommended by Nick in the comments here are some more good resources and information:

• Steve Souder's tips and book:
• Facebook's go-to references when they first optimised their site

update 2

Here's come good stats that shows why page speed is important (source)

• Amazon: 100 ms delay caused a drop in revenue.

• Google: 400 ms delay caused a 0.59% decrease in search requests per user.

• Yahoo!: 400 ms delay caused a 5-9% decrease in traffic.

• Bing: 2 seconds delay caused a 4.3% drop in revenue per user.

• Mozilla made their download page 2.2 seconds faster and was rewarded with an increase of 15.4% in downloads.

• Google Maps reduced the file volume by 30% and observed a 30% increase in map requests.

• Netflix, which uses Appdynamics to monitor their performance, enabled gzip on the server; simply by this single action pages became 13-25% faster and saved 50% of traffic volume!

• Shopzilla succeeded in reducing the loading time from 7 down to 2 seconds, whereby the conversion rate increased by 7-12%, they observed a 25% increase in page requests, they were able to retire 50% of their servers, thus saving energy costs.

• AOL observed the number of page views on several websites. While the fastest users requested 7-8 pages, the slowest only viewed 3-4.

• Edmunds got down from over 10 seconds to less than 2, adding 17% page views and increasing revenue by 3%.