Easy Way To Get Followers On Tumblr?

be ACTIVE, post and reblog lots of pictures. make sure the sources of the photos you post are the link of your blog, people can access to your blog when your photos are exposed to the crowd.
follow "tumblr famous" people. well if you simply want to get more followers, you can follow them or maybe you will gain a few when reblogging their photos or asking them questions, they may publish your ask and your profile will be shown in thousands of dashes.
promote yourself on promotion website or promotion blogs. for example http://tumblrplug.com/ is one of the most popular promotion websites. you can also vote for other people in BOTW or BOTM for an exchange of a promotion.
follow more people, they may follow back. be nice to your followers!

follow people who follow back.
promote yourself on promoblogs.

http://tumblrpop.com/

Post a lot of pics and funny videos of yourself. If people know you, you get publicity.