On Page Optimization: On Page Optimization is the effort you put on the website and is clearly visible, Like:
Optimizing the existing content
HTML code corrections
remove broken / dead links
Add Meta / Alt Tags
Add Google and XML Site Map
Analytic Setup
On Page Optimization should done correctly for any website as it instruct search engine crawlers and spiders about the theme of the website and which keywords you are using to rank on.
On Page Optimization is usually one time practice on the website however, SEO Agency does On Page Optimization after every 3 months(regular interval of time) to keep the site fresh for Search Engines.
Here are few things to do for on page optimization.
1. Analysis and Research of Keywords.
2. Meta Tag Creation specific to page
3. Title Tag (Page Title Optimization)
4. Alt Tag Optimization
5. Optimization of Anchor Tag
6. Placement of Content
7. Keyword Density
8. Implementation of 301 Permanent Redirect
9. Implementation of Google Analytics
10. Search Engine Verification from Google, Yahoo and MSN
11. Submission of XML Sitemap
12. Creation of Proper Link Structure

Off Page Optimization: Off Page Optimization is done offsite and generally not visible on the website however results in driving the ranking higher on search engines. It is a regular process and must be done ethically for better and long-term results. This includes:
Creation of New Pages
Link Building Services
Directory Submission
Article Creation and Submission
Classified Ad Creation and Submission
Blog Post Message Creation and Submission
Press Release Creation and Submission
E-book Creation and Submission.
Here are few things to do for off-page optimisation.
1. Directory Submission
2. Social Bookmarking Submission
3. Blog Posting
4. Blog Hosting
5. Article Submission
6. Press Release Submission
7. Forum Posting
8. Footer Links
9. Associate Marketing
10. Blog Commenting
11. Review Posting
12. Rss Feed Submission
13. Css Submission
14. Video Submission
15. Profile Creation
16. Link Wheel
17. Social Media Optimization