Successful Joomla! Site Checklist

Your website will never look professional with spelling and grammar mistakes. Learn best practices to improve your writing.
Capitalization
Writing Style
Word Variations e.g. UK vs US

Imagine you have developed great responsive template that looks awesome in Safari, but what about those who use Firefox, Chrome or even IE? Have you tested on other OS platforms?
BrowserShots.org
Browserling.com
Spoon.net

You should make sure that all site users land to the same URL whether or not they use www or not. This can be achieved by 301 redirect.
Why use www?
.htaccess Redirect Generator

Think of those who do not use mouse to browse pages or use screen readerS. How comfortable will they feel on your website?
Common problems and solutions
IDI Web Accessibility Checker
Test using a screen reader

Is it easy to read information on your pages? Check your pages for color contrast.
Check color contrast online

Add your site to uptime monitors to track whether your site is still alive.
Uptime robot
GotSiteMonitor.com

Add tracking code to learn your audience and try to understand how they communicate with the site to provide them better service.
Google Analytics
StatCounter
Clicky

Number of mobile users is growing each day, so make sure that your website is friendly enough for mobile devices.
W3C mobile checker

Viewport meta-tag and @viewport rule control layout on mobile browsers. Be sure to use them if you need predictabe behavior.
Don't Forget the Viewport Meta Tag
Make your website mobile friendly

Correct field type will result in correct behavior across platforms and devices. E.g. special characters on screen keyboard for email, or digit keyboard for phone number field.
Input type: Email, Url, Phone
Diving in to HTML5 forms

You do not need to own different types of devices to test your application. Use emulators instead.
Online media query tester
6 free mobile emulators
Opera Mobile Emulator

Google provides a number of rules to optimize your page load. And be sure they use it while ranking your website in search results.
Google Page Speed

There is also a number of parameters you may optimize with tool from Yahoo. Unlike Goole they have documentation that shows how score is calculated.
Yahoo's YSlow

Use the service to find out what can you fix in server response headers to optimize page load.
redbot.org

Both Google and Yahoo recommend to optimize your images. Use following tools to reduce image size without loosing quality.
SmushIt.com
PunyPNG.com
PNGGauntlet for Windows
Image Optim for Mac

Markup pages in ways recognized by major search providers to improve the display of search results.
Schema.org reference
Schema-Creator.org

Check what data is extracted from your pages.
W3C semantic extractor

Make sure you have the latest version of Joomla! If not, update it!
Download latest Joomla!

You may perform periodic checks to be sure that site is clean of malware.
Sucuri SiteCheck

When you develop or customize an extension be sure to protect your site from CSRF attacks.
Explanation and walkthrough

Create a new user, give it super admin permissions, then delete old super admin user for changing ID of the admin user. Since Joomla! 2.5.5 you may change admin name during installation.
Joomla! directions
Recover super admin password

Do not use easy-to-guess passwords. But make them simple to remember.
How to make mnemonic password
Generate mnemonic password

Rename htaccess.txt to .htaccess and make sure RewriteEngine is set to "On".

Do not let automatic scanners find out that you use Joomla by hidding or protecting /administrator/ folder.
Protect a directory with .htaccess
kSecure plugin
JLSecure My Site plugin

To block most common attacks it is suggested to establish advanced security using .htaccess file.
Suggested master .htaccess file
.htaccess redirect generator

Check configuration.php file permissions. Set it to 644, or much better to 444.

If you still on Joomla 1.5.x, do not use the standard jos_ table prefix.

Do not promote that website is built on Joomla! and its version for security reasons.
Remove Joomla generator tag

If you go live with the site being established on development environment, a good idea would be to check /log and /tmp folders paths in "configuration.php"

You do not use them and do not update them. So they are potentially dangerous.
Vulnerable extensions list

Look in your website structure for staging/development files and delete them (.psd, .bak, IDE files, copies etc.)

Show search crawlers what content should be indexed and what should be removed from index.
robots.txt tutorial
Create robots.txt online

Meta data (title, description) should be unique for each page. Use text formatting tags (h1, h2, h3; ul, li, etc). Include keywords into texts – unique for each page if possible. Use images with unique names and fill in alt tags.
How to use HTML meta tags
HTML Formatting Tags
Alt attribute

Once your page is correctly marked up, Rich Snippets will be displayed in Google search results.
Online tester
Getting started
Add authorship

Make use of 404 page by offering useful links and site structure.
A more useful 404

Nowadays favicon is widely used, so be sure to change default Joomla!/template icon to your own one.
Online generator
How to properly link a favicon
Understand favicons

Use SEF extension to get human-readable URLs instead of address line with parameters.
11 best practices for URLs
URL rewrite in Apache