Do you have many interests you could write about?
If you have interests you think others might be interested in, if you were stuck for things to write about, I'd write something about your interests.
Then when ideas come to you from outside of those interests, you already have made posts about those interests so you might hope you have already gained some audience through those posts that might read your posts about other topics.
You might also just find you love writing about your interests and that becomes your main thing which would be cool too.

Another thing you could try is joining a writer's group. You could still afterwards post what you write on Steemit but a writer's group is a good way to get yourself writing something, anything and it also makes you somewhat accountable which makes it more likely to happen. I used to go to a writer's group and we would all suggest a word and then whoever would run the next meeting would choose from those suggestions and we would all write something with that word in it. Sometimes we used whole phrases instead of words and that worked too. It was good and it was an interesting thing to be involved in as the ages involved ranged from people in their 20's through to people in their 70's but we all had a shared common interest - writing. It's certainly a way to get moving.

The other thing is to just write. It's easier said than done but just write about something. I don't have the writer's block type of issues too much because I am someone who thinks a lot which also helps in not running out of things to write about, however I have the issue of being unsure of hte quality of my creations and perhaps being too concerned about that. It's better than thinking your work is amazing and therefore not improving but it's not good to be too down on yourself. This applies to what you wrote as well. If you think your work is amazing, you'll fail because you won't strive to improve it but if you keep being insecure about your writing, you are holding yourself back rather than creating the cool things you will create. Both are harmful mindsets. Keep in mind your writing likely is quite good, but it can use improvement, and that is okay and doesn't mean the world shouldn't see it.

I don't run out of posts to put on Steemit specifically because I also make videos and animations and have various projects going on, but I can see in a more blog style people could run out of things to talk about. I think this is where going to a more stream of consciousness talking about your thoughts on certain issues type of blog might come in. Nothing particularly interesting is happening right now but here are my views on this thing and what do you think, basically.

The best thing you can do if you are unsure about what to write is probably to just write something and suck it and see - it could fall very flat or it could be a post that majorly takes off and is beneficial for you or it might be somewhere in between. Your writing may improve with spending time writing but it won't improve with not writing.