Thanks for your comment
The best way is to create different content from your main site/blog. For example one of my businesses is an embroidery company and the content I publish on the main site that is more article / news / top tips based and the tumblr blog is more visual content which are examples of our recent embroidered and printed work. I link the 2 blogs and promote to help increase traffic from Tumblr back to the main and vice versa.
However don't over do it with keyword anchor on tumbr for the main site as will result in looking spammy and seen to be trying to game the search rankings.
I hope this helps : )
Are you looking to add Tumblr to your social media strategy?