Method 1:
Options +FollowSymlinks
RewriteEngine On
RewriteCond %{HTTP_HOST} ^olddomain.com [NC]
RewriteRule ^(.*)$ http://newdomain.com/$1 [L,R=301]
RewriteCond %{HTTP_HOST} ^www.olddomain.com [NC]
RewriteRule ^(.*)$ http://newdomain.com/$1 [L,R=301]
Method 2:
Options +FollowSymlinks
RewriteEngine On
RewriteCond %{HTTP_HOST} \olddomain.com$
RewriteRule ^(.*)$ http://newdomain.com/$1 [R=301,L]
Method 3:
Options +FollowSymLinks
RewriteEngine on
RewriteRule (.*) http://www.newdomain.com/$1 [R=301,L]
Method 4:
Redirect 301 / http://www.newdomain.com/