For adhesion, I prefer to apply a layer of Kapton/polyamide tape to my print bed. You can get it online in big square sheets — while using the typical 1" or 2" wide rolls one stripe at a time to cover the bed is technically possible, and I did it in the early days, it’s also a monumental pain in the ass and I advise against it if your budget can stretch to an additional two or three dollars to get the square stuff.

Forget glue stick. It’s messy, it produces an uneven thickness, the tubes dry out at inopportune moments, and it’s damn near impossible apply both evenly and also in an area that will actually correctly cover the entire footprint of your part. Instead, use cheap hair spray. Aqua Net seems to work best for me. The stuff in the pink cans; the absolute cheapest variety.

Note that on a Kapton surface your adhesion agent is also a release agent for certain materials, most especially Nylon and to a lesser extent PETG. Having that barrier in between your actual Kapton surface and your part will prevent it from molecularity bonding to your plate the the goddamned sword in the stone, forcing you to say several choice cuss words and re-tape your plate (as well as spend an entertaining afternoon scraping or sanding bits of Kapton tape off of the bottom of your print).

PLA, TPU, ABS/ASA, and polycarbonate can be printed directly onto bare Kapton depending on your level of audacity and/or bravery, especially in the case of the latter two.

Note that you will have to raise your Z offset slightly if you apply tape to your bed. I.e., ideally by the thickness of the tape. You might find that you also want to raise your nozzle about 0.015-0.02mm if you’ve applied a layer of whatever adhesive, and lower it back down after you clean it off. Yes, the infinitesimally thin layer of hair spray will impact your first layer height provided your machine is accurate enough that its first layer offset is not a crapshoot on a per-print basis to begin with.