There are several steps to getting a great first layer but if you break them into sequential steps it is extremely easy to achieve. We will go over each of these steps to get your print off on the right foot:

1. Bed Leveling 
2. Hotend Temperature
   
3. Bed Temperature
   
4. First Layer Speed
5. First Layer Height
6. Fan Speed
7. Calibrating Z-Offset
   

At the end of this guide you will feel confident knowing your first layer will lay down perfect ensuring your print succeeds.

1. Set your print bed to your normal operating temperature before doing any leveling. Heat can alter the level so doing this on a cold bed could give poor results. While your bed is heating verify that the tip of your nozzle is clean from any filament. All filament must be removed from the tip prior to leveling
2. Once the bed is heated and the nozzle is clean, begin the leveling process by running the g-code you generated from our Bed Level Wizard or with your printers built in wizard if it has one.
3. Regardless of which method you choose, the nozzle should "home all" and then go to one of the corners of the bed and lower close to the build surface. Once nozzle has stopped moving, slide a piece of paper between the nozzle and bed. If you are unable to fit paper between them you might need to tighten your bed adjustment knobs to lower the bed until it fits.
4. Wiggle the paper in and out while at the same time loosening the bed adjustment knobs until the paper just starts to get pinched between the nozzle and build surface.
5. Do this for each corner and then verify the center is roughly the same.
6. Repeat this process again until all four corners have the same resistance when paper is placed between the nozzle and bed. You will find that each of the four bed level knobs will need slight adjustments during the second round. This generally takes a minimum of two times going around to get a good level. Note: If you get the four corners level and the center is too low you may need to put a piece of tape under the center of your build surface to compensate for an uneven bed. If it is too high in the middle, you can try flipping the build surface (ex. glass) over and using the tape method.

For this I typically follow the filament manufactures recommendation. If they say that a heated build plate is optional I still turn on my heated bed because it allows the part to pop off on its own after it has cooled when the print is complete. It beats accidentally damaging your print trying to pry it off the build surface. One thing to watch out for is overheating  your bed. This tends to soften the bottom layers causing it to sag which causes the "elephant foot."

90% first layer height? Nope. Regardless of what layer height I am printing with I usually stick with a 0.24mm initial layer height for a 0.4mm nozzle. The exception is for PETG which tends to build up on around the nozzle during the first layer. For PETG I like a first layer height of 0.28mm which seems to help with the build-up issue PETG is known for. There are a lot of users that swear you need to "squish" your first layer with a layer height of less than 0.20mm. This is normally to cover up another issue like incorrect speed or hotend temperature. A thicker layer will hold more heat and allow it to adhere to the surface better before cooling down. Also, a super-thin first layer will likely cause a lot of issues if your printer build plate isn't perfectly flat or your X and Y axis doesn't run completely true.

Regardless of filament type you should always leave your fan off during the first two layers. Again, you want the filament to stay molten as long as possible to allow it to fuse to the build plate to reduce the chances of the part coming off during the print. For filament that does recommend using a fan I like to use the profile below:

Layer 1: 0%

Layer 2: 0%

Layer 3: 50%

Layer 4: 75%

Layer 5+: 100%

I used to think that leveling my bed was the same thing as setting my Z-offset. For years I would assume that by leveling I was at the same time making sure my Z0 was also correct. In order to do this next step, it is necessary to have a set of digital calipers. You can get a nice set off Amazon for cheap. If you are in this hobby for the long haul it is truly an invaluable tool to have. I use mine every day and recommend anyone with a printer to get one. I personally use the Neiko 0-6" Digital Calipers and for around $20 you cannot ask for better. 

After downloading, load the First Layer Test STL file from the downloads section into your slicer to create the g-code for this step. Make sure your first layer height is set to 0.24mm before slicing. If your slicer shows more than one layer in the preview then you have something set incorrectly. This print should only take a few minutes which makes it ideal for doing several iterations if required. Once the print is complete carefully peel it off the build plate and use your digital calipers to measure the layer height in several places. Ideally, you should be close to 0.24mm in all places but if not then you need to adjust your Z-offset. For example, if you measure 0.20mm then you need to raise your Z-offset by 0.04mm. 

Repeat this process until you get a reading close to the First layer height you set of 0.24mm. If you find that your readings are extremely different depending on where you measure on the circle you may need to re-level your bed.

Now that you have tuned your first layer you will find that you very rarely have a failed print. As tempting as it is to just jump into a print, it's a good idea to go through these items before your first print. After many hours of printing, you may also find that you need to revisit some of these adjustments. Things can become uncalibrated from the heat, vibrations, and the force required to remove larger prints. It is usually pretty easy to know when it is time to make adjustments again. You can reference the image below for help identifying when your printers first layer needs work:

-3DMaker Engineering