Hello,
I am marketing manager of an online cryptocurrency casino 'BetSpider' (
https://betspider.io) It has been almost over 1 year since its launch but the revenue is not good.
Most of all, it is very tough to find good places and activities for acquiring new users.
So, I would like to get some advice on the marketing activities for online crypto casinos from you!
Could you please help me?

For your reference, we have an affiliate program! (
https://affiliate.betspider.io/official)
Thanks!
If your casino is eligible to be played for cryptocurrencies, then you can advertise your casino here on Bitcointalk in the Gambling section.
The most popular form of promotion of casinos and bookmakers on this forum (as probably already mentioned by several people) is the Signature Campaign.
Details about the rules for launching such a campaign can be found here:
https://bitcointalk.org/index.php?topic=1684035.0