You can post interesting content that gets reblogged. They’re no secret spice formula to becoming big on Tumblr. Just post new, interesting content (homemade seems to help) and be sure to follow most if not all of the people who follow you (if you’re concerned about getting big that is). Finding people’s AIM, MSN, and Yahoo chat addresses and hitting them up helps. Get to know bits and pieces of the Tumblr community.