Preparing model for 3D printing

Full Article: How to Prepare Your 3D Model for Printing (The Right Way)
Final Checklist Before Printing
Run through this list before you upload:
File opens without errors in at least one program
Dimensions are correct (measured in millimeters)
Mesh is watertight (no holes or non-manifold geometry)
Walls are thick enough (minimum 1.2mm recommended)
File size is reasonable (under 100MB preferred)
No floating geometry or disconnected pieces inside the model
Overhangs are addressed (either support-friendly or designed with chamfers)
Consider Print orientation
Strength (layers are weakest along the Z-axis)
Surface quality (supports leave marks where they attach)
Print success (overhangs over 45° need supports)