At Yahoo Developer network, they have found out 35 best practices to speed up your web site. You can find a resume here next, divided by categories.

Content

1. Make Fewer HTTP Requests
2. Reduce DNS Lookups
3. Avoid Redirects
4. Make Ajax Cacheable
5. Postload Components
6. Preload Components
7. Reduce the Number of DOM Elements
8. Split Components Across Domains
9. Minimize Number of iframes
10. Avoid 404s

Server

1. Use a Content Delivery Network (CDN)
2. Add Expires or Cache-Control Header
3. Gzip Components
4. Configure ETags
5. Flush Buffer Early
6. Use GET for Ajax Requests
7. Avoid Empty Image src

Cookie

1. Reduce Cookie Size
2. Use Cookie-Free Domains for Components

CSS

1. Put Stylesheets at Top
2. Avoid CSS Expressions
3. Choose <link> Over @import
4. Avoid Filters

JavaScript

1. Put Scripts at Bottom
2. Make JavaScript and CSS External
3. Minify JavaScript and CSS
4. Remove Duplicate Scripts
5. Minimize DOM Access
6. Develop Smart Event Handlers

Images

1. Optimize Images
2. Optimize CSS Sprites
3. Do Not Scale Images in HTML
4. Make favicon.ico Small and Cacheable

Mobile

1. Keep Components Under 25 KB
2. Pack Components Into a Multipart Document

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