As a recent member of the 3D Printer owner's club I was having inconsistencies with first layer adhesion. My very first print, a calibration box, printed okay on plain glass but I then looked at other options for PLA printing.
My first try was the basic purple glue stick from Elmer's. I had inconsistent results. Sometimes a print would be okay, sometimes not so much.
So I tried a mix of white glue and water. But apparently the 'washable edible' version of Elmer's glue is not the right kind. I had zero luck with that mix. So I found the old school Elmer's and had better luck with that but printing things like Darth Vader with Cape even with some brims had issues.
So I jumped on the IRC forums that the guys from MakersToolWorks pretty much live on and we got to talking and they recommended 3D Eez. It's on the pricey side but some other internet research, not a lot of sources though, indicated it was good so I ordered some.
It's supposed to be good for non-heated beds but personally I think it would work better for heated beds just based on the difference in holding power between a hot and cool bed that I've seen first hand.
I followed the directions and applied three thin coats letting each one dry, go transparent, before applying the next one and alternating the direction of the coats.
And the results were pretty amazing. At heated bed temps the smallest objects stuck so hard it is pretty much impossible to remove them from the bed. Even small surface area pieces act like they've been epoxied to the bed.
Then when the bed cools down, drops below 28C (ish) degrees the pieces pop off with just a light tap or pry from a spatula.
The material does 'wear' out over time but it does not appear to have anything to do with the number of prints but the amount of time it is heated. I say this because the entire surface faded out on me after about 3/4 of a roll of filament's worth of printing. Whether it was in the center of the bed where most of the prints were or out on the edges, it didn't seem to matter, it went from great adhesion to really bad adhesion and my skirt was just getting dragged around by the nozzle and not sticking at all.
You can run a damp cloth over the surface and get it back to sticking again but from personal experience it didn't get it back to the 'day one' ability to stick.
The material comes off pretty easily under running water water with a paint scraper so clean up isn't a big deal.
Applying it again and everything is back great for first layer adhesion.