On the left is a properly lubricated and axis aligned printer. On the right is a printer without recent lubrication and misaligned axis, resulting in print errors.
A properly leveled build plate is essential for adhesion. A slight slant in relation to the extruder will result in significant enough differences in height by the extremes of the build area to cause a print to fail. Leveling a build plate prior to printing is a common task, and one should get used to doing so on models of printers without automatic plate leveling. Fortunately, time is typically the only cost with build plate leveling.A warped build plat can also cause errors. This is less easy to correct, and depending on the level of warp and the plate material, a replacement plate is sometimes needed.
Improper calibration can result in first layer issues. Printing too low on a plate will result in too thin a first layer, causing issues. Printing too high over the plate will result in the print not having a solid base, likely failing as a result.Poorly calibrated FFF printers are prone to producing a defect in prints known as "Elephant's Foot". This results in a base which is slightly larger then the layers above it. This issue is important for prints where aesthetics and precision are important. For some less important prints (IE: Simple decorations), this defect may be acceptable. However correcting this may still help avoid other more serious calibration issues.