By now you must be aware that in order to rank in a search engine and stay there on the long run, you need to continuously work on the SEO of your website.
To rank better, start with proper On page optimization of all your website SEO tags. Ensure that your pages contain keyword rich H1,H2 tags, a proper title and description which are within the character limit prescribed by Google.
With the ever changing SERP algorithms, now emphasis is more on rich content. So ensure that your website contains rich content which keyword rich as well as not plagiarized.
Periodically monitor your webmaster tools account to check for any errors that might have cropped up and also to keep an eye on the queries on which your page is ranking.
Build high quality backlinks. More than the number of backlinks, its the quality that matters.
Apart from social bookmarking and forum submission, go for classified submissions, directory submissions, Press Release,Submit good quality articles on your subject of expertise to name a few.