For offline traffic, I post flyers or business cards on every pin up corkboard I can find. I have also sponsored rec football and softball teams (team name and jerseys are my website), bumper stickers, T-shirts, and other things. I have fun with it. It would be a lot easier if it wasn’t gambling related, but you can still be creative.
For online traffic, SEO is by far the most important thing you can do to increase traffic.