In the final analysis good quality content will provide for you pretty much everything you might do in terms of SEO/SEM! So, given that you can probably manufacture decent quality content quite easily I'd suggest that you do so, lots, and now!

That does not mean that you can ignore SEO/SEM, I'd not suggest that, but in essence, good quality content on a site that is getting regularly spidered will lead to good results. A short while ago I ran an article directory that was giving me around 4000 see more uniques per day and a revenue to match. Just about the only promotion we did was to add new content to the site every day and ensure that our rss feeds were being used around the interwebs. This is a strategy that I still follow.
I produce good quality content. I place that content on my sites. I syndicate that content around the internet using rss feeds, article directories and blog posting. This generates backlinks and traffic. Along side this we get some bookmarking done by our visitors and of course some additional backlinks as people link to our content.