I mainly do it online. I find Facebook is the best place for me.
I use twitter, and a website called ArtGallery.co.uk (not sure if it is just for UK users only, or not)
I have a blog
http://callyscreations.wordpress.com/I have never had my work in an exhibition and have only ever done 2 craft fairs, although I am doing my first one of the year in March.
I give out a lot of business cards when conversation sparks up about my work too... they are really good to promote :)