What's the first step in troubleshooting a printer or scanner?

First, make sure the power and data cables ( parallel cable or usb cable ) are connected to both the printer or scanner and computer

Check that your Printer and PC are properly connected, may the problem in Cable, If you able to take self test from printer itself then your printer is okay, then you have to troubleshoot with PC, may be the cable faulty or may be you are not using the proper software which required to connect the printer. 

see if that printer has power, if conected  and detected by the computer(OS)

Connect your Computer directly to the printer,Whether it is detecting or not on Computer System.Always check to see if all power codes.Update the printer driver

Powering the device and making sure that its power is on, check if all the cables are connected, check if the driver is properly installed, run an automatic troushoot to check for additional info.

checking power and data cable connection

First check the power connection!!

check if on or off

than check the cable connected to PC

check the driver install or not

than print test page

1.Check the power supply if it is working or not.

2. Check cable(USB/Lan)properly inserted or not

3. Check printer of scanner power on or not

4. Check printer of scanner enable or not

5.Check if software/drivers have been installed.

FIRST CHEK HARDWARE THEN DRIVER OF INSTRUMENT

Check if printer/scanner has power.

Check if all connections are connected.

Check if software/drivers have been installed.

Print test page.