Depending on the 3D modeling software your are using, models can come in on their side or not quite oriented the way you want it to be displayed.
For optimal AR viewing, 3D models should be oriented Y-Axis up. When an object is first placed in the Vusar app, the Z-Axis will be pointing towards your device.
For vertical surfaces (i.e. wall placement), rotate your entire model 90 degrees. This is usually done along the X-Axis. To learn more about vertical surface placed assets, see the following article: 2D to 3D - Creating AR assets from vector files (SVG)