Creating google style urls with .htaccess - php

Question

I am working on creating Google style SEO rules with .htaccess and I am having problems with the final part.
If you type google.com/nexus into your browser you will be redirected to www.google.com/nexus/
It adds www as well as a trailing slash.
How can I achieve this with .htaccess?
#Start rewrite engine
RewriteEngine on
RewriteBase /
# Enforce www
# If you have subdomains, you can add them to
# the list using the "|" (OR) regex operator
RewriteCond %{HTTP_HOST} !^(www|dev|d10|m)\.
RewriteCond %{HTTPS}s ^on(s)|
RewriteRule ^ http%1://www.%{HTTP_HOST}%{REQUEST_URI} [L,R=301]
# Hide the private directory by redirecting the request to index.php
RewriteRule ^(private|\.git) index.php/$1 [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ index.php/$1 [QSA,L]
If you see any places to improve for speed / scalability that would be most appreciated.
My final solution:
RewriteEngine on
RewriteBase /
# Enforce www
# If you have subdomains, you can add them to
# the list using the "|" (OR) regex operator
RewriteCond %{HTTP_HOST} !^(www|dev|d10|m)\.
RewriteCond %{HTTPS}s ^on(s)|
RewriteRule ^ http%1://www.%{HTTP_HOST}%{REQUEST_URI} [R=301,L]
# Add Trailing Slash
RewriteCond %{REQUEST_URI} !(\.[a-zA-Z0-9]{1,5}|/)$
RewriteRule (.*)$ /$1/ [R=301,L]
# Hide the private directory by redirecting the request to index.php
RewriteRule ^(private|\.git) index.php/$1 [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ index.php/$1 [QSA,L]

Answer 1

RewriteCond %{REQUEST_URI} !(\.[a-zA-Z0-9]{1,5}|/)$
RewriteRule (.*)$ http://example.com/$1/ [R=301,L]
Replace example.com with your domain.

Answer 2

RewriteEngine on
RewriteCond %{HTTP_HOST} ^domain\.com
RewriteRule ^(.*)$ http://www.domain.com/$1 [R=permanent,L]
for leading www
http://www.cyberciti.biz/faq/apache-redirect-domaincom-to-wwwdomaincom/