Demonstrating expertise in your field using Q&A sites is a budget-friendly marketing strategy that can drive traffic to your website. Such sites allow the general public to tap the knowledge of the community to get answers to their questions. You gain from the exposure you or brand receives and you typically get a link from your profile back to your site. You can sometimes also reference articles you’ve written as a source, if that’s appropriate.
To make it easier to stay on top of this strategy I recommend you use an RSS reader to subscribe to the most relevant categories for you on your chosen sites and scan them every day or few days to see where you can jump in and contribute.