Make sure the Printer is switched on. Some light (usually green) should indicate the power-on state
Make sure the printer is connected to a working power outlet (test with a different device if unsure)
If the Printer is connected via USB, make sure the USB cable is properly seated (both ends).
If the Printer is connected via Ethernet, make sure the cable is properly seated (both ends).
Check the Ethernet port on the back of the printer, there are usually 1 or 2 lights indicating connectivity.
Make sure your Drivers are up-to-date. Printer drivers are updated frequently.
Verify all the paper-paths are clear. Open printer doors and remove cartridges to make sure there are no bits of paper stuck.
Ink (Ink Jet):
If your printer has been switched off for a long period of time the Cartridges might be dried out. Use a tissue or cotton bud to remove dried Ink.
Reseat Cartridges carefully and let the printer re-initialise.
Prints are smudged (Laser Jet):
The Fuser-Unit may be dirty or broken. This may require replacement.