3D Printing Calibration - How to adjust the steps per unit for X-axis, Y-axis, Z-axis in Marlin Firmware

I recently 3D printed an enclosure for a project and there are several obvious issues with the print.

3D Printing tips and reference info.

Here I keep a list of 3D printing related info. / tips which I find useful.

2015/12/25:

A visual Ultimaker troubleshooting guide
http://support.3dverkstan.se/article/23-a-visual-ultimaker-troubleshooting-guide#scratches

Rafts, Skirts and Brims!
https://www.simplify3d.com/support/tutorials/rafts-skirts-and-brims/