If you're building a printer you designed yourself, awesome.

If you're building a printer someone else designed, good luck ;)

If you're building a kit you purchased, don't be shy about bothering the manufacturer.

If your printer is already fully assembled and ready to go it's still a good idea to skim through here as an educational thing.

General construction
* Read the instructions all the way through before starting
* Keep good notes
* Measure twice, cut once
* Don't take risks with your eyes and hands
* Respect the danger of things that get hot, power tools, and fumes in confined spaces

General printers
* The linear motion elements must be rigid (no flex), consistent (same dimension everywhere), and tough (high wear resistance)
* all moving parts must be properly lubricated
* all fasteners must be properly tightened
* all wires must be secured so that they do not catch on moving parts, rub on edges, or bend too sharply
* anything that heats up must isolated (distance, active cooling or insulation)
* anything that heats up must be allowed to expand and contract

Thermoplastic printers
* anything that comes in contact with molten plastic will probably wear out sooner or later

Cartesian printers
* The X, Y and Z axis must be perfectly aligned
** If there are two linear controls for one axis they must be parallel
** Each axis must be perpendicular