Web tips for improving speed of my website?

Question

Provide some useful tips as

• How can I improve the speed of my website?
• What are the advantages & disadvantages of using sub domains?

Answer 1

use pageSpeed(google) and Yslow(Yahoo) browser's extensions (with firebug or not) for view ALL good pratices for improve your website faster.

For sample : this is a list of good practises checked by Yslow in your Website :

• Minimize HTTP Requests
• Use a Content Delivery Network
• Avoid empty src or href
• Add an Expires or a Cache-Control Header
• Gzip Components
• Put StyleSheets at the Top
• Put Scripts at the Bottom
• Avoid CSS Expressions
• Make JavaScript and CSS External
• Reduce DNS Lookups
• Minify JavaScript and CSS
• Avoid Redirects
• Remove Duplicate Scripts
• Configure ETags
• Make AJAX Cacheable
• Use GET for AJAX Requests
• Reduce the Number of DOM Elements
• No 404s
• Reduce Cookie Size
• Use Cookie-Free Domains for Components
• Avoid Filters
• Do Not Scale Images in HTML
• Make favicon.ico Small and Cacheable

Also, there not advantages or disavantages to use subdomain for speed... But, this can be an advantage or disavantage for SEO, but it is not your question...