For those of you using Tumblr as an Actual Web Site
While I overall still believe in Tumblr's main use as being your blog not your actual website( and Tumblr is more like an extension blog, I don't necessarily feel it should be your main blog) , BUT, Tumblr has come a long way , has many more Themes (templates) and so I can offer these pointers should you decide to use Tumblr as a main website!
If you decide to use Tumblr as a main site they DO allow you the ability to get a customized web link that is my very first most important suggestion!
Next in the Edit Profile Appearance under your settings , you can actually do lots of neat, personalized, customizable things once you have chosen your theme. Simply click Custom HTML, (Tumblr actually has a nice Help section for this, which if you have any coding knowledge or experience can help you create something truly personal)
Try to not use the standard one column Tumblr grid for your items, I suggest picking either columns of 2 or 3.
Choose colors that are easy to read for your Tumblr background and text. I see many Tumblr's that are simply very hard to read or colors that are simply for lack of a better term , UGLY.
CHOOSE A THEME THAT SUPPORTS AND/OR HAS A NAVIGATION MENU BAR !! This is how you are able to make it work like an actual web site.