I've only done it on forums by moderate lurking until a suitable subject comes up and making a hopefully relevant suggestion.

I have a tracking button so I can see how many people are visiting my site. It's encouraging. This does however leave "cookies" on peoples computers which some people think is socially unacceptable.

Within a couple of weeks of being online my webpages somehow got to be top of the Google rankings. Some people don't think much of Google, but I am not too proud to enjoy the hits. I think it got there because it was part of another site which had managed to get a high ranking. When I went solo the ranking seemed to go with me. Visitor numbers continue to increase three years later. The more links you can get to your site from other sites the better, not just because people will use them but because it increases your rank with the search engines. It snowballs.