First things first Tumblr is totally awesome for visual content hence sport teams, before and after gym sessions , then and now interior decorators in fact just about anything that you can create visual content for works well with Tumblr.
So the only thing you really need with Tumblr is a CREATIVE imagination.
Now without any further ado let me explain how to understand and then make the most of Tumblr with this simple guide.

Set Up Your Tumblr

First things first set up your Tumblr account with a good name reflecting what your niche interest or audience is about and use a nice theme that you like. Have a scroll through some other Tumblrs that you like and see their themes and layouts.
This will give you an idea of what you like and don’t like. (Below we discuss how to find Tumblrs you might like)
Search & Tracking

Next thing is use the Tumblr search highlighted below in orange to find your interests simply type in names of celebrities, fashion, music genres pretty much anything you like and then start tracking.

What Tracking means is that all the new content (pictures posts videos etc) related to those interests will keep coming up on your dashboard.
For instance as a young entrepreneur naturally other entrepreneurs would be of interest to me hence I would track and follow content of others in that niche and as such reblog the content that I liked and vice versa.
Not to mention Tumblr will also suggest stuff which you might also like for instance below while I track Entrepreneurs Tumblr suggests business, entreprenurships, and start-ups.
When you follow content, reblog other content and follow other tumblrs you slowly build your own niche Tumblr network they in turn follow and reblog the good content you have and slowly but surely the snowball effect begins .
Your first Tumblr Move.
The basic trick to having a good Tumblr is great content: videos from youtube or any other video networking site, amazing 3D art, breathtaking pictures or just very cool visual content are the basic principles to a good Tumblr pretty much anything that makes you say WOW.
When you make a Tumblr post be it a video, quote, picture makes sure its appropriately tagged with the vocabulary of that particular industry/interest niche for instance fashion tumblr posts, cool stuff posts and entrepreneurial content will all be tagged differently to represent the language of the audience.
The right Tags ensure it can be searched ,tracked and you will be followed by other Tumblrs looking for your type of content.