How do I get popular on tumblr?

[lumos]

There's no real quick way, but there are some things you can do:

Follow a lot of people - about half of them might follow you back (one of my friends follows 2,000 people and has 1,000 followers).
Do "follow for follow" and "promotion for promotion."
Advertise your tumblr on other social sites like your youtube and twitter.
Tag your posts so that they will show up in searches.
Have good interesting blog content (typical "this is how my day went" posts aren't very interesting imo.)
Have a theme to your blog, if you can. It could be a harry potter blog, or a fashion blog, so that people who like those things can follow you.
Whenever you reblog other people's things, add your own comment to the post, so that when it gets reblogged again, your username gets passed around on people's dashboards.

That's all I've got. The longer and more often you're on tumblr, the more followers you gain. Good luck.