Link Building or backlinking is the backbone of modern SEO. Content relevant sites that link to yours are important. It also helps if you have a few links on your website leading to high ranking content relevant websites. Having lots of backlinks from other non related websites is still a good thing but you want to concentrate your efforts on getting backlinks from websites that are related to the content on your website. The quickest and easiest way to get a load of decent backlinks is to shop around on the internet for the websites that will hire text links.
Presuming that you have already submitted your website to all the top search engines and directories, you should keep a check on this regularly to see whats going on with your website URL's. Make any adjustments to optimise each listing, or at the very least the more popular ones. Don't submit to search engines and directories and then forget about it.
Relevant websites, forums, discussion boards or wherever where you can find engaging internet users who are similar minded are a hotbed for solid organic traffic and can in turn lead to higher quality organic listings presuming you have backlinked correctly, and at no time in a way that could be thought of as spam. Also if you are backlinking, remember that the search engines may well include snippets of the text before and after your link, if it looks like a person who is desperately attempting to get users to follow a link to a website, it is unlikely that it will last and probably won't affect your rankings at all.
It's not a secret that if you use Google AdWords, your Ads will show up as listings in search engines long after they have stopped running if they ran long enough because Google caches the pages that your adverts were on. Paid listings can be a fantastic way to get your website out to the right users, this can lead to greater traffic.
Always questioning yourself and your methods, trying new things and trialing different methods is the best way to get ahead of the SEO game. If something is baffling then researching it in depth and taking time to learn is key.