Signature campaign
Indeed a very good way of advertising any casino but sometimes I feel new casinos struggle to maintain the same pay rate as compared to established ones and if they pay less, it's not that effective.
Promotions and giveaways
One of the best possible options of promoting a casino is because it attracts a lot of new players, although there are giveaway abusers always ready to kill most giveaways. But, those can be avoided through wager requirements and maybe KYC if not wager.
I personally feel the best way to promote any casino is to let it run for months smoothly without harassing members for withdrawals and slowly start doing some promotions on Twitter and other social media. It takes time to built trust, you cannot just buy trust with any kind of promotions or bonuses.
Each casino has also to find its own way, because not all customer types will behave in the same manner. If you are going for the masses, you would need to provide a decent service at an affordable price, but if you are whale hunting the focus should be in help, service, usability,... the moment a whale perceives that there is commercial pressure or any sign of untrustworthiness the site is done.