I think along with other things, that content is one of the most imporatnt things that you can focus on, back links do matter, and outbound links also make a difference.
But for just a minute think of it this way, say that you go to web site X and that index page is all confused and jumbled, everything on the page is a parts of the content.
So you go to site X, due to the fact taht you were led there by a search engine, but you look at the site, and the page doesn't really give you any idea about the company or what they do, or how they can help you.
Think of things in the most basic terms, why do I go to a web site, what am I looking to find, if your web site is business related, ask your customers what they'd like to see on your site, give them a way to contact you through a form on your site.
Above all with your content, make 100% sure that your site is easy to navigate, the key Idea is to get your point across in a quick and consice manor, make sure that your visitors can udnerstand what your doing, the best idea is to keep the main point of your site toward the top of your page.
People like things easy to read, and if you ever noticed, it's harder to read form a computer screen then a written page, after a while your eyes start to get tired, so make your point fast, use frases that flow and are easy to read, and people will remember your site and return to it.
You want your main keyword represented form 3 to 6 times throughout your page, and make sure to put it at the top of the first paragraph, and also at the end of the last paragraph.
Also you need to study the SE that your promoting to, like Google places more weight on your <Title> tag then on your keywords in your meta tags, you wnat to make sure that your main keyword is represented at the first of your <Title> tag.
Google does also place a lot of weight on links comeing in to your site, you want quality links that are related to the content of your page, preferadly with a Google pagerank of 5 or more, poor quality links will bring the ranking of your site down, but remember links are a part of your page content.
So if it were me doing it, I would put a lot of time in to creating very high quality content for the very first thing.
Remember this also, it's not how meny links you have comeing in to your site but it's the quality of those links.
When you have people return links to your site, make sure that your main keyword is in those return links.