Hello and thank you! :)
I think that to start off with after creating your writing blog (which is a great idea, by the way), you should follow some other Tumblr writers just to get an idea of their work and how writing blogs work. You can also connect with them, message them, and even do writing collabs with them. I have a list of awesome Tumblr writing blogs here.
Another good idea is to try posting daily on your writing blog. That doesn’t mean that you have to post a poem or a prose piece a day; you could always post a writing piece of your own every other day, and then in the days when you don’t post your own writing, you could reblog a quote or poem or something from someone else.
That way your blog is updated daily and you keep it running.
Good luck c: