Doing SEO in right direction is more important than doing SEO without any deep analysis of website. Traffic and ranking down happen due to new algorithm adopted by Google time to time. I want to suggest you for using social networking and social bookmarking sites for increasing traffic. These are great source of visitors. And use all seo channels to get high serp for your website.
Here is the few list of Google optimization tips for get more traffic to your website.
1) Insert keywords at right place on your meta tags.
2) Name your Images with Descriptive Titles and alt text.
3) Use relevant text on your website.
4) Use Ad sense to assess overall content relevance.
5) Optimize Your Title and Meta tags.
Google page rank depend to update contents, domain age, back links, site structure etc. if you want to huge traffic than use social networking site like facebook, twitter, linkdin etc. apart from use article submission, press release, blog, forum posting, classified ads, if you want potential client than target popular keyword for particular pages on your site in organic pages.
To Increase the pagerank of your site you should submit quailty backlink and higher PR sites, Avoid spaming, Promote your site by useing social networking sites like facebooks, Orkut, yahoo answers, and twiters etc etc You can also use article submission, press release, blog comminting , forum posting, directory submission, classified ads etc etc. By following this you will defiantly increase your ranking.
Most of the SEO is covered by the above members, however I would like to add. Which keywords are you targeting? Always start with a less competitive keyword and once you get ranking for those start targeting the competitive keywords. Also while making backlinks try to use your keywords as the anchor text.
The traffic to your site is decreasing means you need to optimize your site.You follow the SEO steps like On Page Optimization and Off Page optimization for this.First you need to modify the content of your website.Regular updation is important for getting more Page Rank.To get back link, you need to follow the Off page optimization techniques like blog posting, article posting, classified posting, forum posting, directory submission and press release submission.