Sometimes I am handed a STL-file with a model rotated such that is hard to print on a FDM (Fused deposition modeling) type of 3D-printer. Like the heart in this model (created using tinkercad.com):
The model is opened in netfabb Studio Basic 4.9, which is the freeware version. For a FDM type of printer, most of the time, you want the biggest plane facing down. You can do that by performing following steps in netfabb Studio Basic:
Click the 'Align to bottom plane' button from the button bar.
Now rotate the model (right mouse button + move) such that the part you want to be facing down (the backside) is visible. Once it is visible, double click it.
Alakazam: now its back is aligned to the bottom plane. Save it by a right click on the model and select: Export part - as STL.