On Page optimization includes all seo activities which is performed on site to increase serp, page rank and other seo values. While Off page optimization is process to promote sites by using the channels which are not performed on site such as directory submission, article submission etc.
Onpage: Optimize your website content by making it keyword rich. Always write unique and appealing content for your website. Fix all canonical issues of your website and put SEO friendly navigation on your website.
Onpage is all the SEO, keyword, meta tag , heading are done in your website.
Offpage is the SEO is build on the other people website such as create back link on other site such as article submit, Press Release, forum and blog posting, exchange link and so on.
Agree with Johnston- Onpage: Optimize your website content by making it keyword rich. Always write unique and appealing content for your website. Fix all canonical issues of your website and put SEO friendly navigation on your website.
Off page optimization is the tech. like social bookmarking, directory submission, forum, article submission and blog posting which are used to getting ranking in search engine and have quality back links which will increase the traffic a website.
Onpage optimization matters a lot. Since without the page being optimized for the required keyword it is absolutely of no use to do off page optimization. You can start with optimizing the page in the url, meta tags and other html tags
Onpage: All onpage elements including H tags, title tags meta descriptions and most importanly, content. The optimisation of alt tags and image file size to make your site load faster is also considered as onpage SEO.
Offpage: Generating backlinks into your website and using the correct anchor text to increase the relevancy between keyword and website