First of all, you should create a site, if you want to promote casinos, poker rooms from a site.
The site must be a high quality site and very interesting for visitors to have a success in online gambling business.
When you have a good site you’ll be able to register in affiliate programs, and upload their marketing materials to your site.
You’ll have to exchahge links with other webmasters to get a high pagerank.
It’s important to optimize your site for search engines, becuase traffic from search engines is the most important.
There are a lot of things you have to know, so I recommend you to read a lot of articles about SEO, site promotion, to visit forums and learn and learn. There is a lot of information in the Internet.
Good luck!