Petercooper shared a great list here are some of my thoughts...
We failed to promote our last start up very well (Seekler.com), and our new start doesn't rely on eyeballs so we aren't really promoting it. That being said we did learn a few things. Some of these are probably specific to our type of site which was silly / interesting lists, other tips might be more generalizable.
* Focus more niche, whenever we specifically targeted and marketed based around a niche we were far more successful (batman comics vs. comics http://seekler.com/lists/Best+Batman+Graphic+Novels+(Comics) )
* Engage highly motivated users, we wanted to make a great horror movie list and we found a couple horror movie blogs, forums, and fans and got them involved in the process from the beginning and after they all thought it was good we promoted it.
* Time you promotion, some days are better than others to announce a link / site / news. Figure out what days are best for your kind of content. Then try to focus all of the announcements across various sites into one day. Single day focus always did much better for us than slowly stringing along a few links here and there. (likely because of the larger social news and voting effects)
* Get a good relationship with a couple bloggers that write about your topics. We had a few that we could email at any time and they were happy to add a link pointing out our new announcement or release.
* Blog and Twitter we have had a few blog articles drive as much traffic to the site as any marketing attempt. I have also been amazed at how many people will sign up to follow site announcements via twitter if you don't abuse it by posting all the time.
* One in awhile go for something edgy, some of our mainstream lists did well, but some of our weirder ones were easier to get links for.
* Share the wealth if you get some good traffic from other sites link back to people, you will find them more likely to mention something you do if you have been showing them some love.
* Spend a little time making sure you site is OK at SEO, just good enough that you aren't hurting yourself when you do get linked up for various topics.
Anyways just a couple tips off the top of my head, our attempts where never hugely successful but we had a handful of good traffic hear and there. Hope some of my thoughts help.