If Nexus Media Importer is not working in Nexus Tablet follow below steps.
1.Install Nexus Media Importer or Nexus Photo Viewer
2.Under Security -> Lock Screen. Select None
3.Under Accessibility -> Auto-rotate screen. Make sure it is NOT checked
4.Under Language and input -> English (United States),[this step is very important! OTG function will not work with English(UK), I think the designer of Nexus 7 2013 never test new nexus 7 in UK!]
5.Open NMI/NPV manually via the icon.
6.Connect the OTG and Flash/Pen Drive
7.Press and Hold Power until you see “Power Off”
8.Tap OK to Power Off
Repeat steps 7-9 until you see this prompt or NMI opens automatically. If you have repeated this more than 5 times see below. “open Nexus Media importer when this USB device is connected?” Click “OK”.