Hey graham, nice to see you here. I was the guy commenting on your youtube videos, saying you should join steemit.
The best way to gain followers on this platform is to write an introduction post. There is a tag for this kind of posts, it is " introduceyourself ". In this tag, new user starting out on steemit present themselves. Youtubers that do this are welcomed extremely well. Often wales upvote and resteem (equivalent of sharing) their introductory posts and seek interviews because they know that youtube content creators can bring their audiences on steemit. a whale usually has tons of followers, so a resteem from a whale is worth a lot!
Another way to gain exposure on steemit is by using bid bots. This can be a bit complicated if you are just starting out on steemit, but is by far the most effective and easiest way to hit the trending page on steemit.
Being on the trending page will allow HUGE exposure. I personally think that bid bots will be the future of online marketing. Research that if you're interested, or just reply saying that you want an email explaining everything and I'll be happy to send it.
(Of course you could easily announce to your youtube followers that you are posting here but I wrote this with the idea that you don't want to do that until steemit becomes more common for the average youtube user)
Wish you the best on this platform, it will make you forget about all other social media!