I feel the best way of promoting a game is:
Actually have a marketing plan, and one that involves variety.
Even if such may not always be easy to do, with some of us being more developer-minded rather than marketing minded.
Here are some questions to ask yourself when forming a marketing plan:
1. What's in it for others?
2. Will doing this create appeal, or just create noise?
3. How can I do things for others, if I want them to do something for me and play my game?
I realize that my advice may not be the best and most specific there is to offer, and also may not be the right approach for every personality type, but I feel it's a start, and some of these questions have helped me gain a better picture.