There are many competitors in this field. To start, you need to have a good marketing budget.
You can start a bounty and signature campaign on Bitcointalk for your project.
Besides being able to use a signature campaign to spread information about the existence of the casino, casino owners can also take advantage of the forum ad slots auctioned by Theymos by participating in the auction. Promotion of casino advertisements on forum is a great way, but of course it never guarantees the casino will grow big if the owner is not serious about improving its reputation.
Especially for crypto casinos, I think the above two ways of promotion will be able to help them gain attention among forum users sooner or later. Promotion is an important part that will greatly affect the success of the casino getting a lot of users, if the promotion is sustainable the better for their success will be.