SEM - Search Engine Marketing is and internet marketing strategy that will ensure your website will appear on the results page. This approach uses a paid search engine services or pay-per-click advertising.
SMO - Social Media Optimization, using social media to bring traffic into your website, it uses social networking tools or any independent tool that is based on users creative content to achieve better search engine results.
For best results in promoting your website, more than one approach should take place, combining all of them together you can very sure that the rank and position of your website will be improved and search engine indexing will surely result a better position.