1: Z-height. depending on the bed plate this can be very critical to extremely critical. ~0.1mm
2: Bed level. Make your plate flat and level. Level the bed corners and X-gantry (align Z steppers if more than one). Use Automatic Bed Leveling to 'flatten' the bed.
3: Temperature, for PLA Bed 60 and nozzle 200 (check your brand but I always use the same setting for first layer regardless). In your slicer have it drop or raise to your wanted printer temperature after the first layer or so.
4: Speed, you can start at 10mm/s to make it much easier, but aim for 20-30mm/s or be willing to wait forever for the first layer to complete. Build up as you get more proficient at getting a good Z-height and level bed.
5: Some materials are more difficult than others, tape is a good suggestion, even required in some cases (try getting PETG of a smooth glass plate without breaking the glass). However build plate can make all the difference. The textured build plates are much easier to get a good first layer and adhesion. Smooth surfaces are much harder to get started, but can give exceptionally good adhesion if you can get the print to start the first line. Z-height is much more critical on smooth build plates like PEI or glass,
6: Retraction: too slow or too fast and starting lines will be a problem. 25-35mm/s seems good for retract/unretract.
7: Travel speed, too slow and you will ooze too much away between moves to get a good start to lines, especially on the first layer..
8: Skirt or Brim: usually places the nozzle much closer to the actual start of print than purge lines so makes the start of print much easier. Brim adds to overall adhesion too.
9: Fatter lines: using .6 or .8 line width makes laying down the first layer a lot easier. Not as pretty maybe, but easier line starts and better adhesion. Set in slicer to only use wider line for first layer.
Avoid glues, they can help but if your using a BLTouch, for example, you are looking for trouble. So far, the probe tip of a BLTouch is the only thing I have ever found that WILL stick to pritt stick. But generally, if you need glue then something else is wrong.