Efficient Way to management and organize directory

I have new contents to add and update a current site.
As of now, everything is under www.example.com/1stdirectory/content.html.
Since there are so much information, I think it is best to create new .html pages and organize it, rather than adding everything unto that one .html page.


In order to make the site SEO as possible, should I create a 2nd directory and create new html for the new contents?
http://www.example.com/1stdirectory/...ctory/new.html
http://www.example.com/1stdirectory/...ctory/yay.html


Thank you in advance.

Alternative is to not create the 2nd directory but to add new pages like
www.example.com/1stdirectory/newcontent.html
www.example.com/1stdirectory/morecontent.html
www.example.com/1stdirectory/helpcontent.html

and etc.


Wonder which method is best and most recommended.