I assume most people find my app directly on the Mac App Store. There is the "Search App Store..." button that Mac OS displays when you double click an unknown file type. I think that's important for my app, but I have no numbers to back that up.

On the website, I get some hits from fileinfo.com. I also posted to a couple of forums where people asked how to open mdb files on a Mac. I tried to be as little spammy as possible, and always disclosed my affiliation with MDB Viewer when writing about it (for example see http://hintsforums.macworld.com/showthread.php?t=27957 at the bottom of the page)

I provide really thorough documentation on my website. I hope that the docs double as search engine landing pages.

I tried Google Adwords (I got 100€ credit for free), but I don't know if that actually led to any sales. I didn't continue because it seemed too much of a hassle.

I don't do much analytics, so I have no clue how successful the different things I did were. I occasionaly check my website using awstats, and I check app sales with AppViz, and that's about it.