I released the first public demo for One Step From Eden this past weekend. 
Play it on itch.io or below.

I learned a lot.

First, all the things I did WRONG.

• Not having a small audience play the uploaded version.
  • This led to many major bugs being left in (including softlocking the player), please have a small community playtest your game! My Discord and the amazing people in it were invaluable for this. I added them to the credits because of how much they helped.
• Not having an in-game "update available" button
  • How will players know to update their game so they get bug fixes and new content? This was made even more important by #1. (I added in code to check against version text on my website).
    
    
• Putting together a full demo in 3 weeks.
  • Definitely not enough time! I should have put it off at the very least 1 more week, along with constant testing.
    
    
• Not having explicitly unmissable "test mode" notices
  • There were a few times I left test functions available in the releases. Making it so that you can't miss that they are turned on Needs to be a thing.
    
    
• Sending to press/streamers first.
  • Do this after you release and have a working bug-free build, not worth having their content time up with your release date.

Here's what went well:

• Survey button
  • I didn't make the survey button very noticeable, and put it in the corner of the demo screen, but a lot of people still filled it out and not only is the feedback helpful, it can also be very fun to read and motivate you as a developer.
    
    
• Reddit Post
  • Had a semi-popular reddit post on /r/gaming that brought in a lot of people unexpectedly. Unfortunately it got taken down for self promotion because of how often I posted in my game's OSFE subreddit. (Tip: Use a separate account to manage your own game's subreddit to avoid this mixup).
    
    
• Unlockable content
  • Motivates players to keep playing and lets you put in high-level content that would be too much for first-time players. It's a good way to introduce advanced mechanics and things that are "just for fun".
    
    
• Secrets
  • -Secrets are really fun and feel special if not every player finds them! However, I may have made the ones in my game a bit too hidden (many players missed them when making videos), so over a few patches i added some clues about their existence. A few players also seemed to join the community to ask about them which is really cool! I was hoping it would generate some discussion.
    
    
• Analytics
  • I added in analytics before the demo released so that I could see what percentage of players unlocked secrets, how often certain cards were picked (for game balance), and how long players played the game for. I looked to this data a few times for insight on updating the demo.
    
    
• General Response
  • So much positive response from players, I was amazed how much they seemed to enjoy the game and really glad they got excited about it. On the demo end screen I had links to discord and a field to put their email in. I ended up getting hundreds of people interested in the game's release.

Getting the game in the hands of thousands of players is invaluable with all the analytics and feedback you'll receive. A demo gives people a way to enjoy the game and share it, and YouTubers something to actually make content with. I might also recommend getting in touch with the site you're hosting your demo on. They may be able to feature you when/soon after it goes live.