Zen theme - recommended way to display 2 blocks next to each other in a region
Plain old CSS

Plain old css will work. Set your widths with those two blocks and float them.

Zen Grids

If you create custom classes the zen grid sass extension can be used as well to set up layouts using sass

More on zen grids: 


http://zengrids.com/help/
http://thinkshout.com/blog/2013/10/candice/getting-started-sass-drupal-and-zen


Block class

Block Class is a good way of setting blocks up to line up accordingly next to each other:


  Block Class allows users to add classes to any block through the block's configuration interface. By adding a very short snippet of PHP to a theme's block.tpl.php file, classes can be added to the parent  element of a block. Hooray for more powerful block theming!