One thing you can do is write a helpful gambling article and post it on your site then link to it. For example, say you do research on the best House odds in Las Vegas casinos, or maybe you find the best introductory promotions offered by cryptocurrency accepting casinos or you research to find out how people can improve their poker playing skills. Whatever you do try to write something of good value to potential bettors of your site then let others know about the article. If the article is good and valuable enough people will share and link back to it. Then people will be coming to your site for the article and some may hang around to check out other parts of your site.