TL;DR
Most first-layer failures are a greasy bed, not a leveling problem, and skin oil from handling the plate is the usual culprit. Wash a removable plate with warm soapy water, dry it, and stop touching the print surface with bare hands. For a clogged nozzle, heat it and do a cold pull rather than poking it with anything metal.
Safety before anything else
A 3D printer has a heated nozzle that runs well above 400 degrees F and a heated bed that can exceed 200 degrees F.
Power the printer down and let it cool completely before cleaning the bed, the frame, or the fans. The only exception is nozzle work, which requires heat by design and is done deliberately with the printer on and your hands away from the hot end.
Do not use flammable solvents near a hot nozzle. Isopropyl alcohol is flammable, so use it on a cold bed only.
Print in a ventilated room. Some filaments emit more fumes than others, and ventilation is part of routine operation rather than cleaning.
How do you clean a 3D printer bed?
Remove the flexible plate if your printer has one and wash it in warm water with dish soap, scrubbing gently, then rinse and dry with a clean cloth. For a quick clean between prints, wipe the cold bed with isopropyl alcohol on a lint-free cloth. Handle the plate by its edges afterward.
Match the method to the surface
PEI sheets, smooth or textured, are the most common build surface. Warm water and dish soap is the deep clean, since soap removes the oils that alcohol alone leaves behind. Isopropyl alcohol handles quick cleanups. Never use acetone on PEI, which damages it.
Glass beds tolerate soap and water, alcohol, and even a plastic scraper. They are the most forgiving.
Textured powder-coated plates clean with soap and water. Avoid abrasive scrubbing, which flattens the texture that provides adhesion.
Buildtak-style adhesive sheets take alcohol only, and gently. They wear out and are replaced.
Painter's tape or glue stick surfaces are replaced rather than cleaned.
Do not use a metal scraper on any surface except glass, and even then, carefully. Gouges in a print surface become permanent defects in every first layer afterward.
Why does my first layer not stick?
Nine times out of ten the bed is greasy from being touched with bare hands, and skin oil is enough to prevent adhesion. Wash the plate with warm soapy water, dry it, and handle it only by the edges. If it still fails, check bed leveling and nozzle height next.
The habit that prevents most of it
Stop touching the print surface.
Handle a flexible plate by its edges or its tab. Do not press a fingertip on the surface to check for a bump.
Wash the plate with soap and water every ten to twenty prints, and wipe with alcohol between prints if you want a quick refresh.
Keep the plate covered or put away when the printer is idle, because dust settles on it.
Removing stuck prints
Let the bed cool completely first. Most materials release on their own as the plate cools and contracts, and flexing a removable plate pops them off with no tool at all.
If a print is genuinely stuck, use a plastic or a thin flexible metal spatula at a low angle, working around the edges rather than levering from one point.
Do not pry hard. That is how plates get gouged and glass beds crack.
Never use a razor blade toward your hand. Cuts from print removal are a common shop injury.
Nozzle clogs
A cold pull is the standard fix. Heat the nozzle to printing temperature, push filament through by hand, then let it cool to a temperature specific to the material, typically well below the print temperature, and pull the filament out firmly. It brings the debris with it. Repeat until the tip comes out clean.
A nozzle cleaning needle matched to the nozzle diameter can clear a partial blockage from the tip while the nozzle is hot.
Do not use a drill bit or an oversized needle. Enlarging the orifice permanently changes the extrusion width and the nozzle has to be replaced, the same rule that applies to a camp stove jet.
Do not soak an assembled hot end in solvent. Heat blocks, thermistors, and heater cartridges do not tolerate it.
Replace the nozzle when it is worn, which brass nozzles do quickly with abrasive filaments like anything carbon-filled or glow-in-the-dark. Nozzles are inexpensive and replacing one is usually faster than fighting a clog.
Clean the outside of the nozzle with a brass wire brush while the nozzle is hot, keeping the brush away from wiring. Baked-on plastic on the outside eventually drops onto a print.
The rest of the machine
Vacuum or brush dust off the frame, the fans, and the electronics enclosure with the printer off and unplugged. Dust in a fan reduces cooling and causes heat creep, which itself causes clogs.
Wipe the linear rails and rods with a lint-free cloth, then relubricate per the manufacturer with the specified lubricant. Do not use general-purpose penetrating spray on rails.
Clean the extruder gear teeth with a small brush. Filament dust packs into the teeth and causes slipping, which shows as under-extrusion.
Check belts for debris and for tension.
Clean the PTFE tube if your printer has one, and replace it when the end has degraded, which causes clogs at the joint.
Source: Manufacturer maintenance documentation for fused filament fabrication printers
Filament storage, which prevents more problems than cleaning does
Moisture in filament causes popping, stringing, poor layer adhesion, and clogs.
Store filament in sealed containers with desiccant, especially in a damp Oregon winter. Nylon and some other materials absorb moisture within hours of being open.
Dry wet filament in a filament dryer or, where the manufacturer allows it, a low oven at the specified temperature. Do not guess at temperatures, since a spool that softens fuses into a solid block.
Keep a filament dust filter on the feed path in a dusty room.
Where the printer lives
A printer in a dusty garage or a room with pets will need cleaning constantly.
Give it an enclosure or a shelf away from foot traffic. Vacuum the area around it, since purge lines, stringing, and failed prints shed small plastic fragments across the floor.
Keep a bin next to the printer for failed prints and purge waste. Loose fragments of plastic get walked through the house otherwise.
That organized-workspace principle is the same one behind how to clean a sewing machine bobbin case and lint traps, how to clean artist brushes and palettes, and our guide to cleaning tools and equipment around the house.
FAQ
What is the best way to clean a PEI print bed?
Warm water and dish soap, scrubbing gently and rinsing thoroughly, then drying with a clean cloth. Soap removes skin oils that isopropyl alcohol leaves behind, which is why a bed wiped only with alcohol can still fail. Never use acetone on PEI, which damages the surface.
Why is my print not sticking to the bed?
Usually skin oil from handling the plate, which is enough on its own to prevent adhesion. Wash the plate with warm soapy water and handle it only by the edges afterward. If adhesion still fails, check bed leveling, nozzle height, and the first-layer temperature settings next.
How do you unclog a 3D printer nozzle?
Do a cold pull: heat the nozzle to printing temperature, push filament through by hand, cool it to the material's cold-pull temperature, then pull the filament out firmly so it brings the debris with it. Repeat until it comes out clean. Replace a nozzle that stays blocked rather than forcing it.
Can you use a drill bit to clear a nozzle?
No. A drill bit or an oversized needle enlarges the orifice permanently, which changes extrusion width and ruins the nozzle. Use a cleaning needle matched to the nozzle diameter, or do a cold pull. Nozzles are inexpensive, so replacing one is often the faster fix.
How often should you clean a 3D printer?
Wash the print plate every ten to twenty prints and wipe it with alcohol between prints. Vacuum dust off the frame and fans monthly, brush the extruder gear when under-extrusion appears, and check rails and belts on the manufacturer's schedule. Dust in the fans causes heat creep and clogs.
Should you clean the outside of the nozzle?
Yes. Brush baked-on plastic off with a brass wire brush while the nozzle is hot, keeping the brush away from any wiring. Buildup on the outside eventually drops onto a print and ruins it. Take care around the heater cartridge and thermistor wires, which damage easily.
Hobby machines shed dust and plastic into whatever room they live in. If keeping up with the rest of the house is the harder job, get a quote or read more about house cleaning services.