Sitecore has a concept for replacing special characters in a URL. By default, their config file isn’t set to translate spaces. So URLS like, http://www.arkesystems.com/Hello World.aspx translate to http://www.arkesystems.com/Hello%20World.aspx. For SEO purposes, its best to translate spaces. Add the following line to your Sitecore web.configs so the URL would translate to http://www.arkesystems.com/Hello-World.aspx.
<encodeNameReplacements>
<replace mode="on" find="&" replaceWith=",-a-," />
<replace mode="on" find="?" replaceWith=",-q-," />
<replace mode="on" find="/" replaceWith=",-s-," />
<replace mode="on" find="*" replaceWith=",-w-," />
<replace mode="on" find="." replaceWith=",-d-," />
<replace mode="on" find=":" replaceWith=",-c-," />
<replace mode="on" find=" " replaceWith="-" />
</encodeNameReplacements>